regulator: cpr3-regulator: allow use of VDD setpoint in LDO configuration

When the controller is not operating in hardware closed-loop
mode, the driver is aware of the actual VDD supply voltage
setpoint at any given time. If software closed-loop is
enabled, use the VDD supply setpoint as reference voltage
to determine if LDO mode can be safely enabled.

Change-Id: I7c08137279d22b55e271c48833fc2a696c14011a
Signed-off-by: Osvaldo Banuelos <osvaldob@codeaurora.org>