media: mach-pxa: Register the camera sensor fixed-rate clock

The pxa-camera capture driver currently registers a v4l2-clk
clock, named "mclk", to represent the mt9m111 sensor clock.

Register a proper fixed-rate clock using the generic clock framework,
which will allow to remove the v4l2-clk clock in the pxa-camera
driver in a follow-up commit.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Acked-by: Arnd Bergmann <arnd@arndb.de> (for arch/arm/mach-*/)
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>