arm64: zynqmp: rtc: Add calibration

This patch adds the calibration property with required value,
calculated based on rtc input crystal oscillator frequency (32.768Khz).
Signed-off-by: NNava kishore Manne <navam@xilinx.com>
Signed-off-by: NMichal Simek <michal.simek@xilinx.com>

arch/arm/dts/zynqmp.dtsi

@@ -764,6 +764,7 @@
 			interrupt-parent = <&gic>;
 			interrupts = <0 26 4>, <0 27 4>;
 			interrupt-names = "alarm", "sec";
+			calibration = <0x8000>;
 		};
 
 		serdes: zynqmp_phy@fd400000 {