arm: mvebu: armada-xp-theadorable.dts: Add "spi-flash" compatible property

Add the "spi-flash" compatible string so that the generic sf_probe
driver can probe the SPI flash on the theadorable Armada-XP board.
Signed-off-by: NStefan Roese <sr@denx.de>

arch/arm/dts/armada-xp-theadorable.dts

@@ -134,7 +134,7 @@
 					u-boot,dm-pre-reloc;
 					#address-cells = <1>;
 					#size-cells = <1>;
-					compatible = "n25q128a13", "jedec,spi-nor";
+					compatible = "n25q128a13", "jedec,spi-nor", "spi-flash";
 					reg = <0>; /* Chip select 0 */
 					spi-max-frequency = <27777777>;
 				};