media: dt-bindings: media: renesas,csi2: Add r8a77961 support

Add the compatible string for M3-W+ (r8a77961) to the list of supported
SoCs.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
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>