[media] media: add a VEU MEM2MEM format conversion and scaling driver

Video Engine Unit (VEU) is an IP block, found in multiple SuperH and ARM-
based sh-mobile and r-mobile SoCs, capable of processing video data. It
can perform colour-space conversion, scaling and several filtering
transformations. This patch adds an initial implementation of a mem2mem
V4L2 driver for VEU. So far only conversion from NV12 to RGB565 is
supported. Further functionality shall be added in the future.
This driver is based on a VEU vidix driver by Magnus Damm.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>