clk: qcom: gdsc-regulator: Place a 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. This is
required as an interim step before enabling/disabling the
GDSC. Once that's done and the GDSC has latched on to its
new state, remove this voltage vote.

Change-Id: Ibac43bba8248d68f8355d1a9db9cfcbfb9fa7557
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>