staging: vc04_services: Add a V4L2 M2M codec driver

This adds a V4L2 memory to memory device that wraps the MMAL
video decode and video_encode components for H264 and MJPEG encode
and decode, MPEG4, H263, and VP8 decode (and MPEG2 decode
if the appropriate licence has been purchased).

This patch squashes all the work done in developing the driver
on the Raspberry Pi rpi-5.4.y kernel branch.
Thanks to Kieran Bingham, Aman Gupta, Chen-Yu Tsai, and
Marek Behún for their contributions. Please refer to the
rpi-5.4.y branch for the full history.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>