media: i2c: ov9640: drop soc_camera code and switch to v4l2_async

This patch removes the dependency on an obsoleted soc_camera from ov9640
driver and changes the code to be a standalone v4l2 async subdevice.
It also adds GPIO allocations for power and reset signals (as they are not
handled by soc_camera now).

The values for waiting on GPIOs (reset and power) settling down were taken
from the datasheet (> 1 ms after HW/SW reset). The upper limit was chosen
as an arbitrary value. Also one occurrence of mdelay() was changed to
msleep(). The delays were successfully tested on a real hardware.

The patch makes ov9640 sensor again compatible with the pxa_camera driver.

Signed-off-by: Petr Cvek <petrcvekcz@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>