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

Add the compatible string for sc7180 SoC from Qualcomm.

Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20191108092824.9773-8-rnayak@codeaurora.org