dt-bindings: opp: Add qcom-opp bindings with properties needed for CPR

Add qcom-opp bindings with properties needed for Core Power Reduction
(CPR).

CPR is included in a great variety of Qualcomm SoCs, e.g. msm8916 and
msm8996. CPR was first introduced in msm8974.
Co-developed-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Signed-off-by: Niklas Cassel <niklas.cassel@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Documentation/devicetree/bindings/opp/qcom-opp.txt

+Qualcomm OPP bindings to describe OPP nodes
+
+The bindings are based on top of the operating-points-v2 bindings
+described in Documentation/devicetree/bindings/opp/opp.txt
+Additional properties are described below.
+
+* OPP Table Node
+
+Required properties:
+- compatible: Allow OPPs to express their compatibility. It should be:
+  "operating-points-v2-qcom-level"
+
+* OPP Node
+
+Required properties:
+- qcom,opp-fuse-level: A positive value representing the fuse corner/level
+  associated with this OPP node. Sometimes several corners/levels shares
+  a certain fuse corner/level. A fuse corner/level contains e.g. ref uV,
+  min uV, and max uV.