dt-bindings: serial: lantiq: Add optional properties for CCF

Clocks and clock-names are updated in device tree binding.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Songjun Wu <songjun.wu@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>