dt-bindings: clock: Introduce QCOM sc7180 display clock bindings

Add device tree bindings for display clock controller for
Qualcomm Technology Inc's SC7180 SoCs.

Signed-off-by: Taniya Das <tdas@codeaurora.org>
Link: https://lkml.kernel.org/r/1573812245-23827-3-git-send-email-tdas@codeaurora.org
Reviewed-by: Rob Herring <robh@kernel.org>
[sboyd@kernel.org: Add sc7180 to subject]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>