dt-bindings: add compatible string of Allwinner H5 Mali-450 MP4 GPU

Allwinner H5 has a Mali-450 MP4 GPU, which has a reset line like other
Allwinner SoCs with Mali Utgard, but it's a Mali-450, so it needs a new
compatible.

Add the new compatible to Mali Utgard binding document.
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/gpu/arm,mali-utgard.txt

@@ -10,6 +10,7 @@ Required properties:
     * And, optionally, one of the vendor specific compatible:
       + allwinner,sun4i-a10-mali
       + allwinner,sun7i-a20-mali
+      + allwinner,sun50i-h5-mali
       + amlogic,meson-gxbb-mali
       + amlogic,meson-gxl-mali
       + stericsson,db8500-mali
@@ -58,6 +59,10 @@ to specify one more vendor-specific compatible, among:
     Required properties:
       * resets: phandle to the reset line for the GPU
 
+  - allwinner,sun50i-h5-mali
+    Required properties:
+      * resets: phandle to the reset line for the GPU
+
   - stericsson,db8500-mali
     Required properties:
       * interrupt-names and interrupts: