media: dt-bindings: media: amlogic,gx-vdec: add bindings for SM1 family

Add bindings to support the Amlogic Video Decoder on the Amlogic
SM1 family.

SM1 has a slightly different power management handling, thus needing a
separate compatible.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-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>