Add a V4L2 sub-device driver for OmniVision OV4689 image sensor. This
is a 4 Mpx image sensor using the I2C bus for control and the CSI-2
bus for data.

This driver supports following features:
- manual exposure and analog gain control support
- test pattern support
- media controller support
- runtime PM support
- support following resolutions:
  + 2688x1520 at 30 fps

The driver provides all mandatory V4L2 controls for compatibility with
libcamera. The sensor supports 1/2/4-lane CSI-2 modes, but the driver
implements 4 lane mode only at this moment.
Signed-off-by: Mikhail Rudenko <mike.rudenko@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>