media: platform: Add C3 MIPI CSI-2 driver

Add a driver for the CSI-2 receiver unit found on the Amlogic C3 SoC.

Create a drivers/media/platform/amlogic/c3/ directory to host the driver
and the forthcoming support for the Amlogic C3 MIPI adapter and C3 ISP.

This driver is used to receive the MIPI data from image sensor.

Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Keke Li <keke.li@amlogic.com>
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
[hverkuil: fix typo: uinit -> unit]