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.