Add support for communicating with the SCP firmware, which will be used
by MT8183.

[acourbot: refactor, cleanup and split]
[hverkuil: fixed some checkpatch alignment warnings]
Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Co-developed-by: Alexandre Courbot <acourbot@chromium.org>
Signed-off-by: Alexandre Courbot <acourbot@chromium.org>
Acked-by: Tiffany Lin <tiffany.lin@mediatek.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>