arm64: dts: meson-g12b-odroid-n2: add SPIFC controller node

Add disabled SPIFC controller node with instruction on how to enable
it while lowering capabilities of the eMMC controller from 8bits bus
width to 4bits bus width, it's data pins 4 to 7 being shared with
the SPI NOR controller pins.
Signed-off-by: NNeil Armstrong <narmstrong@baylibre.com>
Signed-off-by: NKevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20200313090713.15147-5-narmstrong@baylibre.com

arch/arm64/boot/dts/amlogic/meson-g12b-odroid-n2.dts

@@ -451,6 +451,27 @@
 	vqmmc-supply = <&flash_1v8>;
 };
 
+/*
+ * EMMC_D4, EMMC_D5, EMMC_D6 and EMMC_D7 pins are shared between SPI NOR pins
+ * and eMMC Data 4 to 7 pins.
+ * Replace emmc_data_8b_pins to emmc_data_4b_pins from sd_emmc_c pinctrl-0,
+ * and change bus-width to 4 then spifc can be enabled.
+ * The SW1 slide should also be set to the correct position.
+ */
+&spifc {
+	status = "disabled";
+	pinctrl-0 = <&nor_pins>;
+	pinctrl-names = "default";
+
+	mx25u64: spi-flash@0 {
+		#address-cells = <1>;
+		#size-cells = <1>;
+		compatible = "mxicy,mx25u6435f", "jedec,spi-nor";
+		reg = <0>;
+		spi-max-frequency = <104000000>;
+	};
+};
+
 &tdmif_b {
 	status = "okay";
 };