This is prerequisite for enabling the sub-device node.

The control handler is now initialized in driver's probe callback
in order to allow the user space access controls before the device
power is enabled with s_power. This is needed due to s_power being
currently called only by the host driver.

It also adds the subdev internal operations, only open() for now
for the TRY format initialization.
Acked-by: HeungJun Kim <riverful.kim@samsung.com>
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>