media: ad5820: Add support for ad5821 and ad5823

According to the datasheet, both AD5821 and AD5820 share a compatible
register-set:
http://www.analog.com/media/en/technical-documentation/data-sheets/AD5821.pdf

Some camera modules also refer that AD5823 is a replacement of AD5820:
https://download.kamami.com/p564094-OV8865_DS.pdf



Suggested-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Ricardo Ribalda Delgado <ribalda@kernel.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>