arm64: dts: phycore-imx8mm: fix nor mtd partitions

Add #address-cells and #size-cells properties to som_flash. This
enables correct parsing of added SPI NOR mtd partition child nodes that
are set in the bootloader.
Signed-off-by: Yannic Moog <y.moog@phytec.de>
Signed-off-by: Cem Tenruh <c.tenruh@phytec.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mm-phycore-som.dtsi

@@ -102,6 +102,8 @@ &flexspi {
 	status = "okay";
 
 	som_flash: flash@0 {
+		#address-cells = <1>;
+		#size-cells = <1>;
 		compatible = "jedec,spi-nor";
 		reg = <0>;
 		spi-max-frequency = <80000000>;