Add a V4L2 sub-device driver for the Sony IMX208 image sensor.
This is a camera sensor using the I2C bus for control and the
CSI-2 bus for data.

[Sakari Ailus: Rename sensor async register function to make it compile,
	       use exposure_max and wrap a few long lines.]
Signed-off-by: NPing-Chung Chen <ping-chung.chen@intel.com>
Signed-off-by: NYeh, Andy <andy.yeh@intel.com>
Signed-off-by: NShawn Tu <shawnx.tu@intel.com>
Reviewed-by: NTomasz Figa <tfiga@chromium.org>
Signed-off-by: NSakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab+huawei@kernel.org>