Replace g/s_mbus_fmt ops with the pad level get/set_fmt operations.
Add media entity initialization and set subdev flags so the host driver
creates a subdev device node for the driver.
A mutex was added for serializing the subdev operations. When setting
format is attempted during streaming an (EBUSY) error will be returned.

After the device is powered up it will now remain in "power sleep"
mode until s_stream(1) is called. The "power sleep" mode is used
to suspend/resume frame generation at the sensor's output through
s_stream op.
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>