media: uapi: Document PiSP Compressed RAW Bayer formats

Document the Raspberry Pi compressed RAW Bayer formats.

The compression algorithm description is provided by Nick Hollinghurst
<nick.hollinghurst@raspberrypi.com> from Raspberry Pi.

Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>