media: staging: max96712: Add support for 3-lane C-PHY

Add basic support for outputting the test patterns on a 3-lane CSI-2
C-PHY bus. As the driver only can output frames form its internal test
pattern generator, enabling C-PHY output is as simple as setting the
output mode to C-PHY instead of D-PHY.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
[Sakari Ailus: Wrap long lines.]
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>