ARM: dts: Add board-specific compatible string to npcm750-evb devicetree

According to the revised binding, the devicetree needs a board-specific
compatible string.
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Link: https://lore.kernel.org/r/20210320164023.614059-2-j.neuschaefer@gmx.netSigned-off-by: Joel Stanley <joel@jms.id.au>

arch/arm/boot/dts/nuvoton-npcm750-evb.dts

@@ -9,7 +9,7 @@
 
 / {
 	model = "Nuvoton npcm750 Development Board (Device Tree)";
-	compatible = "nuvoton,npcm750";
+	compatible = "nuvoton,npcm750-evb", "nuvoton,npcm750";
 
 	aliases {
 		ethernet2 = &gmac0;