cpufreq: qcom-hw: Simplify counting frequency domains

For quite some time, this driver has been performing some quite
low-level DT operations. Simplify that using platform_get_resource.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Reviewed-by: Bjorn Andersson <andersson@kernel.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>