The sensor needs the MCLK clock running when it's being probed. On
platforms where the sensor is instantiated from a DT (MMP2) it is going
to happen asynchronously.

Therefore, the current modus operandi, where the bridge driver fiddles
with the sensor power and clock itself is not going to fly. As the comments
wisely note, this doesn't even belong there.

Luckily, the ov7670 driver is already able to control its power and
reset lines, we can just drop the MMP platform glue altogether.

It also requests the clock via the standard clock subsystem. Good -- let's
set up a clock instance so that the sensor can ask us to enable the clock.
Note that this is pretty dumb at the moment: the clock is hardwired to a
particular frequency and parent. It was always the case.
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>