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

The S3C RTC requires 32768 Hz clock as input which is provided by PMIC.
However there is no such clock provider but rather a regulator driver
which registers the clock as a regulator.  This is an old driver which
will not be updated so add a workaround - a fixed-clock to fill missing
clock phandle reference in S3C RTC.

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/20200907161141.31034-11-krzk@kernel.org

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

@@ -32,6 +32,13 @@ memory@30000000 {
 			0x40000000 0x18000000>;
 	};
 
+	pmic_ap_clk: clock-0 {
+		/* Workaround for missing clock on PMIC */
+		compatible = "fixed-clock";
+		#clock-cells = <0>;
+		clock-frequency = <32768>;
+	};
+
 	regulators {
 		compatible = "simple-bus";
 		#address-cells = <1>;
@@ -228,6 +235,11 @@ buck4_reg: BUCK4 {
 					regulator-always-on;
 				};
 
+				ap32khz_reg: EN32KHz-AP {
+					regulator-name = "32KHz AP";
+					regulator-always-on;
+				};
+
 				vichg_reg: ENVICHG {
 					regulator-name = "VICHG";
 				};
@@ -326,6 +338,11 @@ &uart3 {
 	status = "okay";
 };
 
+&rtc {
+	clocks = <&clocks CLK_RTC>, <&pmic_ap_clk>;
+	clock-names = "rtc", "rtc_src";
+};
+
 &sdhci0 {
 	bus-width = <4>;
 	non-removable;