[Patch] [Enhancement] Add udev rule for Wii U GameCube Adapter

[flibitijibibo]

Your system information

• Steam client version:
• SteamOS version: 2.121
• Opted into Steam client beta?: No
• Opted into SteamOS beta?: No
• Have you checked for updates in Settings > System?: Yes

Please describe your issue in as much detail as possible:

Not much to see here, just this udev rule:

SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="057e", ATTRS{idProduct}=="0337", MODE="0666"

This comes from Dolphin's documentation for Wii U GameCube Adapter support. This allows applications to access the adapter directly, since there is currently no joystick driver in the kernel. At the moment, other than Dolphin, this is only used by the program listed in the repro steps to produce a virtual device via uinput. As a bonus, the program includes an SDL_GameController entry for the virtual device created! It's a decent solution until a driver is made or the Steam Controller subsystem adds native support for GameCube controllers, thereby allowing SteamOS to officially support the most important controller of our generation.

Steps for reproducing this issue:

1. Download and compile this program
2. Grant user access to uinput
3. Plug in adapter, run!

[flibitijibibo]

This is now required for SDL 2.0.12's upcoming support for GameCube controllers.