clk: qcom: gdsc: Support for min operational vote on GDSC parent

For GDSCs that reside on domains that are collapsible and support a
minimum voltage of retention, explicitly vote on the minimal operating
voltage, LowSVS for the rail during enable and remove the vote before
disabling the regulator.

Change-Id: I3b2d414ae9696f9376136600f6160b96dd987fc7
Signed-off-by: Taniya Das <tdas@codeaurora.org>