clk: qcom: regmap: Add regmap support for voltage voting

Add support for prepare, unprepare, pre and post rate change regmap
clk_ops callback functions for regmap clocks to handle regulator
requirements.

Change-Id: If4657adcc047e1ca005d3d4f7ab88146dba85ee0
Signed-off-by: David Dai <daidavid1@codeaurora.org>