Add variant to IMX8M to enable G2/HEVC codec.
Define the capabilities for the hardware up to 3840x2160.
G2 doesn't have a postprocessor, uses the same clocks and has it
own interrupt.

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