soc: qcom: add API for matching voltages across CPUs

Create an API to match voltages across asymmetric CPUs as
this can be useful in systems with a shared rail across CPUs.
The API takes in one input argument which is the frequency of
a big cluster CPU for which a voltage-equivalent little cluster
CPU frequency is desired. The return value is this little
cluster CPU frequency. All frequencies are in units of kHz.

Change-Id: I821819a0761566984dd7f92014599ff0fcb85e90
Signed-off-by: Amir Vajid <avajid@codeaurora.org>