media: i2c: Add ROHM BU64754 Camera Autofocus Actuator

Add support for the ROHM BU64754 Motor Driver for Camera Autofocus. A
V4L2 Subdevice is registered and provides a single
V4L2_CID_FOCUS_ABSOLUTE control.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>