media: hantro: Support color conversion via post-processing

The Hantro G1 decoder is able to enable a post-processor
on the decoding pipeline, which can be used to perform
scaling and color conversion.

The post-processor is integrated to the decoder, and it's
possible to use it in a way that is completely transparent
to the user.

This commit enables color conversion via post-processing,
which means the driver now exposes YUV packed, in addition to NV12.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>