cpufreq: qcom: Read voltage LUT and populate OPP

Add support to read the voltage look up table and populate OPP for all
corresponding CPUS for consumers like the energy model could use the
frequency and voltage from the OPP tables. Also update the logic to not add
duplicate OPPs.

Tested-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Taniya Das <tdas@codeaurora.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>