media: imx-mipi-csis: Use GENMASK for all register field masks

Multiple register field mask macros use GENMASK, while other define the
mask value manually. Standardize on GENMASK everywhere, as well as on
the _MASK suffix to name the macros. This improves consistency and helps
with readability.

No functional change is intended.

Link: https://lore.kernel.org/r/20250822002734.23516-7-laurent.pinchart@ideasonboard.com


Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>