dt-bindings: gpu: mali-midgard: Add resets property

The Amlogic ARM Mali Midgard requires reset controls to power on and
software reset the GPU, adds these as optional in the bindings.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

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

@@ -37,6 +37,20 @@ Optional properties:
 - operating-points-v2 : Refer to Documentation/devicetree/bindings/opp/opp.txt
   for details.
 
+- resets : Phandle of the GPU reset line.
+
+Vendor-specific bindings
+------------------------
+
+The Mali GPU is integrated very differently from one SoC to
+another. In order to accomodate those differences, you have the option
+to specify one more vendor-specific compatible, among:
+
+- "amlogic,meson-gxm-mali"
+  Required properties:
+  - resets : Should contain phandles of :
+    + GPU reset line
+    + GPU APB glue reset line
 
 Example for a Mali-T760: