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

Convert qcom-nvmem-cpufreq to DT schema format, splitting it into
an OPP schema and a CPUFreq schema in the process.

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>