dt-bindings: qcom,pdc: Add compatible for SM8250

Add the compatible string for SM8250 SoC from Qualcomm. This compatible
is used already in DTS files but not documented yet

Signed-off-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210115090941.2289416-1-vkoul@kernel.org