New VdpYCbCr Formats VDP_YCBCR_FORMAT_Y_U_V_444 and,
VDP_YCBCR_FORMAT_Y_UV_444 have been added in VDPAU with libvdpau-1.2
to be used in get/putbits for YUV 4:4:4 surfaces. Earlier mapping of
AV_PIX_FMT_YUV444P to VDP_YCBCR_FORMAT_YV12 is not valid.

Hence this Change maps AV_PIX_FMT_YUV444P to VDP_YCBCR_FORMAT_Y_U_V_444
to access the YUV 4:4:4 surface via read-back API's of VDPAU.