media: ov9640: Use the generic clock framework

Commit 63839882 ("media: mach-pxa: palmz72/pcm990: remove soc_camera dependencies")
removed the last in-tree user of this sensor. New users
will be required to use the generic clock framework,
so it's possible to convert the driver to use it.

Convert the driver to use the CCF, and drop the legacy
v4l2-clk API.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Acked-by: Petr Cvek <petrcvekcz@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>