arm: qcom: dts: gic: add compatible string for Qualcomm MSM GICs

Document the Qualcomm MSM GICs implementation as compatible with the
ARM GIC standard.
Signed-off-by: Kumar Gala <galak@codeaurora.org>
Signed-off-by: Olof Johansson <olof@lixom.net>

Documentation/devicetree/bindings/arm/gic.txt

@@ -18,6 +18,8 @@ Main node required properties:
 	"arm,arm11mp-gic"
 	"brcm,brahma-b15-gic"
 	"arm,arm1176jzf-devchip-gic"
+	"qcom,msm-8660-qgic"
+	"qcom,msm-qgic2"
 - interrupt-controller : Identifies the node as an interrupt controller
 - #interrupt-cells : Specifies the number of cells needed to encode an
   interrupt source.  The type shall be a <u32> and the value shall be 3.