media: dt-bindings: media: rockchip-vdec: add RK3228 compatible

Document the RK3228 compatible for rockchip-vdec.
Also add the optional assigned-clocks and assigned-clock-rates
properties.

Signed-off-by: Alex Bee <knaerzche@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>