media: staging: atomisp: use clock framework for camera clocks

The Atom ISP driver initializes and configures PMC clocks which are
already handled by the clock framework.

Remove all legacy vlv2_platform_clock stuff and move to the clk API to
avoid conflicts, e.g. with audio machine drivers enabling the MCLK for
external codecs

Fixes: a49d2536

 ("staging/atomisp: Add support for the Intel IPU v2")

Tested-by: Carlo Caione <carlo@endlessm.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>