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 fixed-clock.  This fixes S3C RTC and
silences dtbs_check warnings like:
  arch/arm/boot/dts/exynos4412-tiny4412.dt.yaml: rtc@
10070000: clocks: [[7, 346]] is too short
  arch/arm/boot/dts/exynos4412-tiny4412.dt.yaml: rtc@
10070000: clock-names: ['rtc'] is too short
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200830135200.24304-32-krzk@kernel.org
                        compatible = "samsung,clock-xusbxti";
                        clock-frequency = <24000000>;
                };
+
+               pmic_ap_clk: pmic-ap-clk {
+                       /* Workaround for missing clock on PMIC */
+                       compatible = "fixed-clock";
+                       #clock-cells = <0>;
+                       clock-frequency = <32768>;
+               };
        };
 
        panel {
 
 &rtc {
        status = "okay";
+       clocks = <&clock CLK_RTC>, <&pmic_ap_clk>;
+       clock-names = "rtc", "rtc_src";
 };
 
 &sdhci_2 {