This allows me to reduce the set of formats supported by the renderers to the most optimal set, for a nice speed boost.

--HG--
rename : src/video/SDL_yuv_mmx.c => src/render/SDL_yuv_mmx.c
rename : src/video/SDL_yuv_sw.c => src/render/SDL_yuv_sw.c
rename : src/video/SDL_yuv_sw_c.h => src/render/SDL_yuv_sw_c.h
rename : src/video/mmx.h => src/render/mmx.h