Add support for C-PHY on R-Car V4H. While the V4H supports both D-PHY
and C-PHY this patch only adds support for the C-PHY mode due to lack of
documentation and hardware to test on.

The V4H is the first Gen4 device that is enabled in the rcar-csi2
driver. There is much overlap with the Gen3 driver, the primary
difference is in how the receiver is started. The V4H have a much larger
register space and some addresses overlap with Gen3.

[Sakari Ailus: Use div_u64() to divide a 64-bit integer.]
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@kernel.org>