dt-bindings: opp: qcom-opp: Convert to DT schema

Convert qcom-opp.txt to DT schema format.

Signed-off-by: Yassine Oudjana <y.oudjana@protonmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>