arm: mvebu: Add SPI flash on Armada XP-DB board

This patch add support for the SPI flash M25P64 which is present on
the Armada XP DB board. This flash stores the bootloader and its
environment.
Signed-off-by: NGregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: NJason Cooper <jason@lakedaemon.net>

arch/arm/boot/dts/armada-xp-db.dts

@@ -109,5 +109,17 @@
 		usb@d0052000 {
 			status = "okay";
 		};
+
+		spi0: spi@d0010600 {
+			status = "okay";
+
+			spi-flash@0 {
+				#address-cells = <1>;
+				#size-cells = <1>;
+				compatible = "m25p64";
+				reg = <0>; /* Chip select 0 */
+				spi-max-frequency = <20000000>;
+			};
+		};
 	};
 };