[media] Add v4l2 subdev driver for S5K4ECGX sensor

This patch adds driver for Samsung S5K4ECGX image sensor with an
embedded SoC ISP. The driver only implements preview operation mode
and still capture (snapshot) and face detection features are missing
now. Following controls are supported: contrast, saturation,
brightness, sharpness.

Signed-off-by: Sangwook Lee <sangwook.lee@linaro.org>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>