media: rcar-vin: Extend group notifier DT parser to work with any port

The R-Car VIN group notifier will be extend to support a new group of
subdevices, the R-Car ISP channel selector in addition to the existing
R-Car CSI-2 receiver subdevices.

The existing DT parsing code can be reused if the port and max number of
endpoints are provided as parameters instead of being hard-coded. While
at it align the group notifier parser function names with the rest of
the driver.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>