dt-bindings: remoteproc: mediatek: Add optional memory-region to mtk,scp

The SCP co-processor can optionally be passed a reserved memory region
to use. Add this property in the dt-binding.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220511195452.871897-3-nfraprado@collabora.com


Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>