clk: qcom: add vdd-class voltage regulator voting support

Add support to manage voltage supply regulators via the
vdd-class voting interface.  Provide functions that can be
easily used to implement clk_ops callbacks used for voltage
voting.

Change-Id: I891b5944ed8075074c11f139d9e6951d796c7f90
Signed-off-by: David Collins <collinsd@codeaurora.org>
Signed-off-by: David Dai <daidavid1@codeaurora.org>