Detect and use SDL2 with help of this Dolphin CMake module:
https://github.com/dolphin-emu/dolphin/blob/master/CMakeTests/FindSDL2.cmake
Look for SDL_gamecontroller.h instead of SDL.h to prevent CMake from
using SDL1 include dirs
Update to SDL2
Update native submodule
Merge branch 'master' into sdl2

Conflicts:
	native
Add T2 and T3 to our register enum for clarity
Merge branch 'sdl2' of github.com:PGGB/ppsspp into PGGB-sdl2
Rebase RadarNyan work on Generate version while build on Wiondows
Merge branch 'windows-exe-version' of https://github.com/RadarNyan/ppsspp into verbuild

Conflicts:
	Windows/version.rc