media: ov5693: add support for acpi clock-frequency prop

Add support for ACPI-based platforms that specify the clock frequency by
using the "clock-frequency" property instead of specifying a clock
provider reference

Signed-off-by: Tommaso Merciai <tommaso.merciai@amarulasolutions.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>