The imx219 camera is capable of either two-lane or four-lane
operation.  When operating in four-lane, both the pixel rate and
link frequency change. Regardless of the mode, however, both
frequencies remain fixed.

Helper functions are needed to read and set pixel and link frequencies
which also reduces the number of fixed registers in the table of modes.
Signed-off-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>