media: dt-bindings: media: venus: Add sc7280 dt schema

Add a schema description for the venus video encoder/decoder on
the sc7280.

Signed-off-by: Dikshita Agarwal <dikshita@codeaurora.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>