regulator: cpr3-regulator: impose APM restriction for HW closed-loop only

APM switching must occur when the VDD supply voltage crosses the
APM threshold voltage.  When using hardware closed-loop mode,
the VDD supply voltage may vary anywhere between the CPR floor
and ceiling voltages.  This means that it could cross the APM
threshold without changing the APM setting.  When using software
closed-loop mode, the cpr3-regulator driver can correctly switch
the APM when crossing the APM threshold voltage inside of the CPR
interrupt handler.

Therefore, modify the cpr3-regulator driver so that the CPR floor
to ceiling voltage range is only trimmed based upon the APM
threshold voltage when operating in hardware closed-loop mode.

Change-Id: If012d9c384faa84658d29745508c656033553146
Signed-off-by: David Collins <collinsd@codeaurora.org>