regulator: spm-regulator: Add additional settling delay for FTS2.5 SMPS

Based on characterization add 70us settling delay on the voltage UP
to account for warm-up time and ramp-up delays for 0-10% and 90-100%
of the voltage value.

On the voltage ramp-down side add the stepper slew-rate delay and
and an additional 70us margin to avoid voltage updates while the
stepper is in progress. This could lead to voltage over/undershoot
due to buck-internal synchronization failure.

CRs-Fixed: 1036738
Change-Id: Id4230be9c4c981758bbf6860bab1f487a3b57f85
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>