dt-bindings: qcom,pdc: Add compatible for sc7180

Add the compatible string for sc7180 SoC from Qualcomm.

Signed-off-by: Rajendra Nayak <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Reviewed-by: Stephen Boyd <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/devicetree/bindings/interrupt-controller/qcom,pdc.txt

···
 - compatible:
 	Usage: required
 	Value type: <string>
-	Definition: Should contain "qcom,<soc>-pdc"
+	Definition: Should contain "qcom,<soc>-pdc" and "qcom,pdc"
+		    - "qcom,sc7180-pdc": For SC7180
 		    - "qcom,sdm845-pdc": For SDM845
 
 - reg: