msm: krait-regulator: add support for auto mode

On certain PMIC the AUTO mode for the ganged regulator operates
within spec. Allow the driver to use the auto mode and skip
controlling  PFM/PWM mode switching.

Enable support for using auto mode configuration.

Change-Id: Id4b0b39e0022496844a5f5bc1a37e4795ddd9c5b
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>