media: verisilicon: Add film grain feature to AV1 driver

Film grain feature add "old style" grain noise on decoded streams.
Grain noise is applied after decoding by the postprocessor.
The level of grain is based on gaussian sequence.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>