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.

Note that this fix-up patch has been squashed in:
commit c7d3dc884292 ("clk: qcom: gdsc: Fix issue with
dereferencing NULL pointer in gdsc APIs").

Change-Id: Ibac43bba8248d68f8355d1a9db9cfcbfb9fa7557
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>
[collinsd@codeaurora.org: squashed in a fix-up patch]
Signed-off-by: David Collins <collinsd@codeaurora.org>