msm: board-8974: Switch from stub to krait regulator for 8841 S5-S8

Remove stub-regulator devices and initialization for PMIC PM8841 FTSMPS
regulators S5-S8. Add a krait-regulator initialization call so that the
krait-regulator driver is used to control these regulators instead of
the stub-regulator driver.

Change-Id: I6f1ea43acf435c48f7f5224234d95af9502f15d2
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>