clk: qcom: clk-voter: Add support for voter clocks

Voter clocks nodes would require aggregation of all child node rates.
Certain clocks that are not rate-settable can still take
advantage of voter clock functionality.

Change-Id: Ibab7a5aa6aa89236974fcd0d65ffe0bd1a7acb12
Signed-off-by: Taniya Das <tdas@codeaurora.org>