arm64: dts: imx8mn-evk: add QSPI flash

There is a 32MiB Micron MT25QU256ABA1 serial NOR flash on the EVK board.
Add a device tree node for it.

Tested on a 8MNANOD3L-EVK.
Signed-off-by: Michael Walle <michael@walle.cc>
Tested-by: Heiko Thiery <heiko.thiery@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mn-evk.dtsi

@@ -110,6 +110,22 @@ vddio: vddio-regulator {
 	};
 };
 
+&flexspi {
+	pinctrl-names = "default";
+	pinctrl-0 = <&pinctrl_flexspi>;
+	status = "okay";
+
+	flash0: flash@0 {
+		compatible = "jedec,spi-nor";
+		reg = <0>;
+		#address-cells = <1>;
+		#size-cells = <1>;
+		spi-max-frequency = <166000000>;
+		spi-tx-bus-width = <4>;
+		spi-rx-bus-width = <4>;
+	};
+};
+
 &i2c1 {
 	clock-frequency = <400000>;
 	pinctrl-names = "default";
@@ -267,6 +283,17 @@ MX8MN_IOMUXC_SAI2_RXC_GPIO4_IO22	0x19
 		>;
 	};
 
+	pinctrl_flexspi: flexspigrp {
+		fsl,pins = <
+			MX8MN_IOMUXC_NAND_ALE_QSPI_A_SCLK               0x1c2
+			MX8MN_IOMUXC_NAND_CE0_B_QSPI_A_SS0_B            0x82
+			MX8MN_IOMUXC_NAND_DATA00_QSPI_A_DATA0           0x82
+			MX8MN_IOMUXC_NAND_DATA01_QSPI_A_DATA1           0x82
+			MX8MN_IOMUXC_NAND_DATA02_QSPI_A_DATA2           0x82
+			MX8MN_IOMUXC_NAND_DATA03_QSPI_A_DATA3           0x82
+		>;
+	};
+
 	pinctrl_gpio_led: gpioledgrp {
 		fsl,pins = <
 			MX8MN_IOMUXC_NAND_READY_B_GPIO3_IO16	0x19