dt-bindings: media: venus: Add sm8250 dt schema

Add a schema description for the venus video encoder/decoder on the sm8250.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210215160254.1572615-3-bryan.odonoghue@linaro.org