media: imx274: use regmap_bulk_write to write multybyte registers

Currently 2-bytes and 3-bytes registers are set by very similar
functions doing the needed shift & mask manipulation, followed by very
similar for loops setting one byte at a time over I2C.

Replace all of this code by a unique helper function that calls
regmap_bulk_write(), which has two advantages:
 - sets all the bytes in a unique I2C transaction
 - removes lots of now unused code.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>