clk: qcom: clk-rcg2: add callbacks to deal with voltage voting

Specify prepare, unprepare and pre/post rate change callbacks for all
clk-rcg2 clk_ops.  This ensures that supply regulator requirements are
managed properly at runtime.

Change-Id: I6d7e31983e99c2ef9f546771d7046e8f0111debc
Signed-off-by: David Dai <daidavid1@codeaurora.org>