Wii U: Support For Seperate Gamepad and TV Audio Devices

[Fangal-Airbag]

This PR adds in support for separate Gamepad and TV SDL Devices while retaining support for mirroring the audio on both at the same time.

These audio devices can be created as follows:

// Gamepad
SDL_AudioDeviceID drcAudio = SDL_OpenAudioDevice(SDL_AUDIO_DEVICE_WIIU_GAMEPAD, 0, &desiredSpec, &obtainedSpec1, 0);

// TV
SDL_AudioDeviceID tvAudio = SDL_OpenAudioDevice(SDL_AUDIO_DEVICE_WIIU_TV, 0, &desiredSpec, &obtainedSpec2, 0);

// Both
SDL_AudioDeviceID bothAudio = SDL_OpenAudioDevice(SDL_AUDIO_DEVICE_WIIU_MIRRORED, 0, &desiredSpec, &obtainedSpec3, 0);

When setting up SDL_Audio and creating an audio device, if not specified, the audio device will default to SDL_AUDIO_DEVICE_WIIU_MIRRORED.

sorry for the second PR, had to fix some git stuff

[GaryOderNichts]

Thanks for the PR! Hmm, this code seems somewhat fragile at the moment.
Closing a single audio device will uninitialize AX, even if other devices are still running. wiiuDevices is also not updated when closing a device, causing potential issues in the frame callback.
Ideally it should be possible to close and reopen audio devices. I think separating the AX initialization from opening and closing audio devices might be a good idea.

[Fangal-Airbag]

So with this commit AX will only deinitialize if its the last audio device being closed. wiiuDevices is also now updated with both the open and close device functions. AX will also not initialize if its already been initialized, this was already the case before this PR but this case should only really happen now. Let me know if I missed anything!