ARM: dts: lager: Add CEC clock for HDMI transmitter

The adv7511 on the Lager board has a 12 MHz fixed clock
for the CEC block. Specify this in the dts to enable CEC support.

Based on a similar patch for Koelsch by Hans Verkuil.
Signed-off-by: NNiklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Tested-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7790-lager.dts

@@ -669,11 +669,19 @@
 		};
 	};
 
+	cec_clock: cec-clock {
+		compatible = "fixed-clock";
+		#clock-cells = <0>;
+		clock-frequency = <12000000>;
+	};
+
 	hdmi@39 {
 		compatible = "adi,adv7511w";
 		reg = <0x39>;
 		interrupt-parent = <&gpio1>;
 		interrupts = <15 IRQ_TYPE_LEVEL_LOW>;
+		clocks = <&cec_clock>;
+		clock-names = "cec";
 
 		adi,input-depth = <8>;
 		adi,input-colorspace = "rgb";