[media] exynos4-is: Add common FIMC-IS image sensor driver

This patch adds a common image sensor driver and Makefile/Kconfig
to enable compilation of the whole IS driver.
The sensor subdev driver currently only handles an image sensor's
power supplies and reset signal. There is no I2C communication as
it is handled by the ISP's firmware.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>