cpufreq: qcom-nvmem: Simplify driver data allocation

Simplify the allocation and cleanup of driver data by using devm
together with a flexible array. Prepare for adding additional per-CPU
data by defining a struct qcom_cpufreq_drv_cpu instead of storing the
opp_tokens directly.

Signed-off-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>