arm64: dts: imx8mn-ddr4-evk: Describe the 32.768 kHz PMIC clock

The ROHM BD71847 PMIC has a 32.768 kHz clock.

Describe the PMIC clock to fix the following boot errors:

bd718xx-clk bd71847-clk.1.auto: No parent clk found
bd718xx-clk: probe of bd71847-clk.1.auto failed with error -22

Based on the same fix done for imx8mm-evk as per commit
a6a355ede574 ("arm64: dts: imx8mm-evk: Add 32.768 kHz clock to PMIC")

Fixes: 3e44dd09736d ("arm64: dts: imx8mn-ddr4-evk: Add rohm,bd71847 PMIC support")
Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

[ upstream commit: 0310b5aa0656a94102344f1e9ae2892e342a665d ]
diff --git a/src/arm64/freescale/imx8mn-ddr4-evk.dts b/src/arm64/freescale/imx8mn-ddr4-evk.dts
index 7dfee71..d8ce217 100644
--- a/src/arm64/freescale/imx8mn-ddr4-evk.dts
+++ b/src/arm64/freescale/imx8mn-ddr4-evk.dts
@@ -59,6 +59,10 @@
 		interrupts = <3 IRQ_TYPE_LEVEL_LOW>;
 		rohm,reset-snvs-powered;
 
+		#clock-cells = <0>;
+		clocks = <&osc_32k 0>;
+		clock-output-names = "clk-32k-out";
+
 		regulators {
 			buck1_reg: BUCK1 {
 				regulator-name = "buck1";