media: v4l: Add HEXTILE compressed format

Add HEXTILE compressed format which is defined in Remote Framebuffer
Protocol (RFC 6143, chapter 7.7.4 Hextile Encoding) and is used by
Encoding Compression Engine (ECE) present on Nuvoton NPCM SoCs.

Signed-off-by: Marvin Lin <milkfafa@gmail.com>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>