ARM: dts: am437x-idk: Fix QSPI compatible string

Unlike Linux kernel, U-Boot depends on "spi-flash" compatible to probe
m25p80 spi-nor devices. Hence, add "spi-flash" compatible string to
m25p80 node. Without this patch, flash device DT data is not parsed and
QSPI operates in unsupported mode leading to data corruption.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>

arch/arm/dts/am437x-idk-evm.dts

@@ -341,7 +341,7 @@
 
 	spi-max-frequency = <48000000>;
 	m25p80@0 {
-		compatible = "mx66l51235l";
+		compatible = "mx66l51235l", "spi-flash";
 		spi-max-frequency = <48000000>;
 		reg = <0>;
 		spi-cpol;