qcom-cpufreq: Cache the resolved frequency index

This driver implements resolved_freq and target methods.
Since target method does not know the resolved frequency
index, the frequency table look up is needed again. We
can optimize this by caching the resolved frequency
index in the resolved_freq method.

Change-Id: Ib303ef57c51ce50de52b759728bc8c162a90dc29
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>