st/va: add conversion for yv12 to nv12in putimage v2

st/va: add conversion for yv12 to nv12in putimage v2

For putimage call, if image format is yv12 (or IYUV with U V field swap) and
surface format is nv12, then we need to convert yv12 to nv12 and then copy
the converted data from image to surface. We can't use the existing logic
where surface is destroyed and re-created with yv12 format.

v2 (chk): fix some compiler warnings and commit message

Signed-off-by: Boyuan Zhang <boyuan.zhang@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>