dt-bindings: msm:disp: add sc7180 DPU variant

Add a compatible string to support sc7180 dpu version.
Signed-off-by: Kalyan Thota <kalyan_t@codeaurora.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>

Documentation/devicetree/bindings/display/msm/dpu.txt

@@ -8,7 +8,7 @@ The DPU display controller is found in SDM845 SoC.
 
 MDSS:
 Required properties:
-- compatible: "qcom,sdm845-mdss"
+- compatible:  "qcom,sdm845-mdss", "qcom,sc7180-mdss"
 - reg: physical base address and length of contoller's registers.
 - reg-names: register region names. The following region is required:
   * "mdss"
@@ -41,7 +41,7 @@ Optional properties:
 
 MDP:
 Required properties:
-- compatible: "qcom,sdm845-dpu"
+- compatible: "qcom,sdm845-dpu", "qcom,sc7180-dpu"
 - reg: physical base address and length of controller's registers.
 - reg-names : register region names. The following region is required:
   * "mdp"