fix(morello): dts: use documented DPU compatible string

The official Arm Komeda DPU DT binding only mentions the "arm,mali-d71"
string as a possible compatible string. The D32 version is just a
variant of the D71, and the revision can and will be auto-detected at
runtime.
Add the usual fallback compatible string scheme to contain a documented
compatible string.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Change-Id: Ic1eade122b030dc983944b161eec175facf75357

fdts/morello-soc.dts

@@ -160,7 +160,7 @@
 	dp0: display@2cc00000 {
 		#address-cells = <1>;
 		#size-cells = <0>;
-		compatible = "arm,mali-d32";
+		compatible = "arm,mali-d32", "arm,mali-d71";
 		reg = <0 0x2cc00000 0 0x20000>;
 		interrupts = <0 69 4>;
 		interrupt-names = "DPU";