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: Nava kishore Manne <navam@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/arch/arm/dts/zynqmp.dtsi b/arch/arm/dts/zynqmp.dtsi
index f2c0b5e..951e069 100644
--- a/arch/arm/dts/zynqmp.dtsi
+++ b/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 {