media: dt-bindings: Add binding doc for i.MX8QXP and i.MX8QM ISI

Add binding documentation for i.MX8QXP and i.MX8QM ISI. The clock-names,
power-domains, and ports differ significantly from the existing
nxp,imx8-isi.yaml. Create a new file to avoid complex if-else branches.

Add new file to MAINTAINERS.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20250522-8qxp_camera-v5-1-d4be869fdb7e@nxp.com


Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>