dt-bindings: clock: mediatek: add g3dsys bindings

Add bindings to g3dsys providing necessary clock and reset control to
Mali-450.
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

Documentation/devicetree/bindings/arm/mediatek/mediatek,g3dsys.txt

+MediaTek g3dsys controller
+============================
+
+The MediaTek g3dsys controller provides various clocks and reset controller to
+the GPU.
+
+Required Properties:
+
+- compatible: Should be:
+	- "mediatek,mt2701-g3dsys", "syscon":
+		for MT2701 SoC
+	- "mediatek,mt7623-g3dsys", "mediatek,mt2701-g3dsys", "syscon":
+		for MT7623 SoC
+- #clock-cells: Must be 1
+- #reset-cells: Must be 1
+
+The g3dsys controller uses the common clk binding from
+Documentation/devicetree/bindings/clock/clock-bindings.txt
+The available clocks are defined in dt-bindings/clock/mt*-clk.h.
+
+Example:
+
+g3dsys: clock-controller@13000000 {
+	compatible = "mediatek,mt7623-g3dsys",
+		     "mediatek,mt2701-g3dsys",
+		     "syscon";
+	reg = <0 0x13000000 0 0x200>;
+	#clock-cells = <1>;
+	#reset-cells = <1>;
+};