platform: msm: qcom_geni_se: Support to identify SE clock frequency

When multiple execution environments share a serial engine, they have
to identify and program the operating frequency requirement of that
execution environment.

Add support to identify a required frequency from the list of operating
frequencies for a serial engine.

Change-Id: I35fb49ed4ae15fe964bca72a0680f430ad95a6dc
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>