Add support for BGR888 image format.

No existing media bus codes describe exactly the way data is transferred
on the CSI-2 bus. This is not a new issue, the CSI-2 YUV422 8-bit format
is described by MEDIA_BUS_FMT_UYVY8_1X16 which is an arbitrary
convention and not an exact match. Use the MEDIA_BUS_FMT_BGR888_1X24 to
follow the same convention, based on the order in which bits are
transmitted over the CSI-2 bus when producing images in RGB24 format.
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>