ARM: dts: s5pv210: add RTC 32 KHz clock in SMDKV210

The S3C RTC requires 32768 Hz clock as input which is provided by PMIC.
However the PMIC is not described in DTS at all so at least add
a workaround to model its clock with a fixed-clock.

This fixes dtbs_check warnings:

  rtc@e2800000: clocks: [[2, 145]] is too short
  rtc@e2800000: clock-names: ['rtc'] is too short
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200907161141.31034-15-krzk@kernel.org

arch/arm/boot/dts/s5pv210-smdkv210.dts

@@ -31,6 +31,13 @@ memory@20000000 {
 		reg = <0x20000000 0x40000000>;
 	};
 
+	pmic_ap_clk: clock-0 {
+		/* Workaround for missing PMIC and its clock */
+		compatible = "fixed-clock";
+		#clock-cells = <0>;
+		clock-frequency = <32768>;
+	};
+
 	ethernet@18000000 {
 		compatible = "davicom,dm9000";
 		reg = <0xA8000000 0x2 0xA8000002 0x2>;
@@ -147,6 +154,8 @@ &uart3 {
 
 &rtc {
 	status = "okay";
+	clocks = <&clocks CLK_RTC>, <&pmic_ap_clk>;
+	clock-names = "rtc", "rtc_src";
 };
 
 &sdhci0 {