chore: make yuzu REUSE compliant

[REUSE] is a specification that aims at making file copyright
information consistent, so that it can be both human and machine
readable. It basically requires that all files have a header containing
copyright and licensing information. When this isn't possible, like
when dealing with binary assets, generated files or embedded third-party
dependencies, it is permitted to insert copyright information in the
`.reuse/dep5` file.

Oh, and it also requires that all the licenses used in the project are
present in the `LICENSES` folder, that's why the diff is so huge.
This can be done automatically with `reuse download --all`.

The `reuse` tool also contains a handy subcommand that analyzes the
project and tells whether or not the project is (still) compliant,
`reuse lint`.

Following REUSE has a few advantages over the current approach:

- Copyright information is easy to access for users / downstream
- Files like `dist/license.md` do not need to exist anymore, as
  `.reuse/dep5` is used instead
- `reuse lint` makes it easy to ensure that copyright information of
  files like binary assets / images is always accurate and up to date

To add copyright information of files that didn't have it I looked up
who committed what and when, for each file. As yuzu contributors do not
have to sign a CLA or similar I couldn't assume that copyright ownership
was of the "yuzu Emulator Project", so I used the name and/or email of
the commit author instead.

[REUSE]: https://reuse.software

Follow-up to 01cf05bc75b1e47beb08937439f3ed9339e7b254

6 files changed, 12 insertions, 18 deletions

diff --git a/src/input_common/helpers/stick_from_buttons.cpp b/src/input_common/helpers/stick_from_buttons.cpp
index 31e6f62ab..536d413a5 100644
--- a/src/input_common/helpers/stick_from_buttons.cpp
+++ b/src/input_common/helpers/stick_from_buttons.cpp
@@ -1,6 +1,5 @@
-// Copyright 2017 Citra Emulator Project
-// Licensed under GPLv2 or any later version
-// Refer to the license.txt file included.
+// SPDX-FileCopyrightText: 2017 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
 
 #include <chrono>
 #include <cmath>
diff --git a/src/input_common/helpers/stick_from_buttons.h b/src/input_common/helpers/stick_from_buttons.h
index 437ace4f7..e8d865743 100644
--- a/src/input_common/helpers/stick_from_buttons.h
+++ b/src/input_common/helpers/stick_from_buttons.h
@@ -1,6 +1,5 @@
-// Copyright 2017 Citra Emulator Project
-// Licensed under GPLv2 or any later version
-// Refer to the license.txt file included.
+// SPDX-FileCopyrightText: 2017 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
 
 #pragma once
 
diff --git a/src/input_common/helpers/touch_from_buttons.cpp b/src/input_common/helpers/touch_from_buttons.cpp
index f1b57d03a..da4a3dca5 100644
--- a/src/input_common/helpers/touch_from_buttons.cpp
+++ b/src/input_common/helpers/touch_from_buttons.cpp
@@ -1,6 +1,5 @@
-// Copyright 2020 Citra Emulator Project
-// Licensed under GPLv2 or any later version
-// Refer to the license.txt file included.
+// SPDX-FileCopyrightText: 2020 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
 
 #include <algorithm>
 #include "common/settings.h"
diff --git a/src/input_common/helpers/touch_from_buttons.h b/src/input_common/helpers/touch_from_buttons.h
index 628f18215..c6cb3ab3c 100644
--- a/src/input_common/helpers/touch_from_buttons.h
+++ b/src/input_common/helpers/touch_from_buttons.h
@@ -1,6 +1,5 @@
-// Copyright 2020 Citra Emulator Project
-// Licensed under GPLv2 or any later version
-// Refer to the license.txt file included.
+// SPDX-FileCopyrightText: 2020 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
 
 #pragma once
 
diff --git a/src/input_common/helpers/udp_protocol.cpp b/src/input_common/helpers/udp_protocol.cpp
index cdeab7e11..994380d21 100644
--- a/src/input_common/helpers/udp_protocol.cpp
+++ b/src/input_common/helpers/udp_protocol.cpp
@@ -1,6 +1,5 @@
-// Copyright 2018 Citra Emulator Project
-// Licensed under GPLv2 or any later version
-// Refer to the license.txt file included.
+// SPDX-FileCopyrightText: 2018 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
 
 #include <cstddef>
 #include <cstring>
diff --git a/src/input_common/helpers/udp_protocol.h b/src/input_common/helpers/udp_protocol.h
index 889693e73..d9643ffe0 100644
--- a/src/input_common/helpers/udp_protocol.h
+++ b/src/input_common/helpers/udp_protocol.h
@@ -1,6 +1,5 @@
-// Copyright 2018 Citra Emulator Project
-// Licensed under GPLv2 or any later version
-// Refer to the license.txt file included.
+// SPDX-FileCopyrightText: 2018 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
 
 #pragma once