arm64: dts: imx8mm-phg: Disable flexspi

The imx8mm-tqma8mqml SoM used on the PHG board does not come with
the QSPI flash populated, so disable it to avoid the following
error message:

spi-nor spi3.0: unrecognized JEDEC id bytes: 00 00 00 00 00 00
Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mm-phg.dts

@@ -111,6 +111,11 @@ panel_out_bridge: endpoint {
 	};
 };
 
+/* QSPI is not populated on the SoM */
+&flexspi {
+	status = "disabled";
+};
+
 &ecspi1 {
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_ecspi1>;