media: hantro: Simplify postprocessor

Add a 'postprocessed' boolean property to struct hantro_fmt
to signal that a format is produced by the post-processor.
This will allow to introduce the G2 post-processor in a simple way.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>