regulator: qpnp-labibb: change the LAB soft start time for TTW mode

As per the requirement, LAB soft start time should be configured
to 200us when touch-to-wakeup (TTW) mode is activated. Save and
restore the LAB_SOFT_START_CTL register setting before entering
TTW mode and after exiting TTW mode, similar to IBB register
settings done before.

CRs-Fixed: 928619
Change-Id: Ib285cbb11a788a23726b2cbbb2954d2ac62db171
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>