media: On Semi AR0521 sensor driver

The driver has been extensively tested in an i.MX6-based system.
AR0521 is a 5.7 mm x 4.3 mm, 5 MPix RGGB MIPI/HiSPi BSI CMOS sensor
from On Semiconductor.

Signed-off-by: Krzysztof Hałasa <khalasa@piap.pl>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>