Optimized 7 funcs with LSX and LASX:
1. yuy2ToUV_c
2. yvy2ToUV_c
3. uyvyToUV_c
4. nv12ToUV_c
5. nv21ToUV_c
6. abgrToA_c
7. rgbaToA_c

Reviewed-by: colleague of Shiyou Yin
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>