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

Add a driver for the Unicam camera receiver block on BCM283x processors.
Compared to the bcm2835-camera driver present in staging, this driver
handles the Unicam block only (CSI-2 receiver), and doesn't depend on
the VC4 firmware running on the VPU.

The commit is made up of a series of changes cherry-picked from the
rpi-5.4.y branch of https://github.com/raspberrypi/linux/

 with
additional enhancements, forward-ported to the mainline kernel.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reported-by: kbuild test robot <lkp@intel.com>