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>

Documentation/devicetree/bindings/serial/lantiq_asc.txt

@@ -6,8 +6,23 @@ Required properties:
 - interrupts: the 3 (tx rx err) interrupt numbers. The interrupt specifier
   depends on the interrupt-parent interrupt controller.
 
+Optional properties:
+- clocks: Should contain frequency clock and gate clock
+- clock-names: Should be "freq" and "asc"
+
 Example:
 
+asc0: serial@16600000 {
+	compatible = "lantiq,asc";
+	reg = <0x16600000 0x100000>;
+	interrupt-parent = <&gic>;
+	interrupts = <GIC_SHARED 103 IRQ_TYPE_LEVEL_HIGH>,
+		<GIC_SHARED 105 IRQ_TYPE_LEVEL_HIGH>,
+		<GIC_SHARED 106 IRQ_TYPE_LEVEL_HIGH>;
+	clocks = <&cgu CLK_SSX4>, <&cgu GCLK_UART>;
+	clock-names = "freq", "asc";
+};
+
 asc1: serial@e100c00 {
 	compatible = "lantiq,asc";
 	reg = <0xE100C00 0x400>;