[media] rockchip/rga: v4l2 m2m support

Rockchip RGA is a separate 2D raster graphic acceleration unit. It
accelerates 2D graphics operations, such as point/line drawing, image
scaling, rotation, BitBLT, alpha blending and image blur/sharpness

The driver supports various operations from the rendering pipeline.
 - copy
 - fast solid color fill
 - rotation
 - flip
 - alpha blending

The code in rga-hw.c is used to configure regs according to operations
The code in rga-buf.c is used to create private mmu table for RGA.

Signed-off-by: Jacob Chen <jacob-chen@iotwrt.com>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>