media: dt-bindings: media: nxp,imx7-csi: Add i.MX8MM support

The i.MX8MM integrates a CSI bridge IP core, as the i.MX7. There seems
to be no difference between the two SoCs according to the reference
manual, but as documentation may not be accurate, add a compatible
string for the i.MX8MM, with a fallback on the compatible i.MX7.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>