msm: krait-regulator-pmic: workaround for soft start issue

There is hw bug in FTS2 where if the gang is disabled and enabled in a
single phase configuration, the subsequent addition of phases do not see
the SS done flag of the gang leader and as a result use SS_CTL timings
for voltage stepping instead of VS_CTL settings.

The sw workaround is to update SS_CTL to the same timing as VS_CTL when
phases are added. Also when the gang is disabled switch back to original
SS_CTL to allow for quick startup when enabled.

Moreover, the recommended settling time after a phase increase with this
workaround is 100uS instead of 50uS. Update the code for this as well.

CRs-Fixed: 640655
Change-Id: I732b526152e581231af19b4aac05b1500a68712e
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>