drm/fourcc: Add RGB161616 and BGR161616 formats

Add FourCC definitions for the 48-bit RGB/BGR formats to the
DRM/KMS uapi.

The format will be used by the Raspberry Pi PiSP Back End,
supported by a V4L2 driver in kernel space and by libcamera in
userspace, which uses the DRM FourCC identifiers.

Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Rob Clark <robin.clark@oss.qualcomm.com>
Reviewed-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Link: https://lore.kernel.org/r/20240226132544.82817-1-jacopo.mondi@ideasonboard.com


Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>