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.

In addition, this does not allow creating frames contexts with sw_format
for which no known transfer formats exist. In theory, we should check
whether the chroma format (i.e. the sw_format) is supported at all by
the vdpau driver, but checking for transfer formats has the same effect.

Note that the pre-existing code adds 1 to priv->nb_pix_fmts[i] for
unknown reason, and some checks need to account for that to check for
empty lists. They are not off-by-one errors.

Also remove the redundant casts which were hiding the error here.

(cherry picked from commit 7081620a)

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

Also remove the redundant casts which were hiding the error here.