media: rcar-csi2: Abstract PHTW and PHYPLL register offsets

media: rcar-csi2: Abstract PHTW and PHYPLL register offsets

Most of the registers used on the R-Car V4M CSI-2 IP are shared with the
devices already supported by the rcar-csi2 driver. Two registers which
function and layout are the same are however found on different offsets.

Prepare for adding support for R-Car V4M by storing the offset to these
two registers offsets in the device information structured. This way the
code, which is shared between the devices, can be reused when V4M
support is added.

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