media: bcm2835-unicam: Driver for CCP2/CSI2 camera interface

Add driver for the Unicam camera receiver block on
BCM283x processors.

This commit is made up of a series of changes cherry-picked from the
rpi-4.19.y branch.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Naushir Patuck <naush@raspberrypi.com>