OPP: Introduce dev_pm_opp_find_freq_{ceil/floor}_indexed() APIs

In the case of devices with multiple clocks, drivers need to specify the
clock index for the OPP framework to find the OPP corresponding to the
floor/ceil of the supplied frequency. So let's introduce the two new APIs
accepting the clock index as an argument.

These APIs use the exising _find_key_ceil() helper by supplying the clock
index to it.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
[ Viresh: Rearranged definitions in pm_opp.h ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>