media: verisilicon: AV1: Be more flexible with postproc capabilities

The RK3588 post-processor block is able to convert 10-bit pixel-formats
into 8-bit pixel-formats.

Fixes: 003afda9 ("media: verisilicon: Enable AV1 decoder on rk3588")
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Sebastian Fricke <sebastian.fricke@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>