st/va/postproc: reallocate interlaced destination buffer

st/va/postproc: reallocate interlaced destination buffer

When the source buffer is progressive source, re-allocate the
destination buffer as progressive if it isn't already - otherwise
transcoding will fail.

Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/1418
Signed-off-by: Thong Thai <thong.thai@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4001>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4001>