media: hantro: postproc: Introduce struct hantro_postproc_ops

Turns out the post-processor block on the G2 core is substantially
different from the one on the G1 core. Introduce hantro_postproc_ops
with .enable and .disable methods, which will allow to support
the G2 post-processor cleanly.

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