media: rcar-vin: Move and rename CSI-2 link notifications

The CSI-2 link notifications are no longer the only option for the VIN
group. Change the symbol prefix to rvin_csi2_ for all CSI-2 specific
code and move the link notification code to the correct section not to
mix it with the soon to be added R-Car ISP channel selector notification
helpers.

There is no functional change and apart from the symbol prefix change
all functions are moved verbatim.

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>