ARM: dts: qcom: add mode control for S12B regulator for Lahaina

PMIC PM8350 SMPS regulator S12B is a parent of several LDO
regulators.  Barring an application processor mode request, the
S12B mode transitions from AUTO to retention when entering AOSS
sleep.  This can cause brown-outs if any of the child LDOs is
drawing significant current.

Add mode control support for S12B so that application processor
consumers can vote to keep S12B in AUTO mode when needed.  This
avoids power faults during AOSS sleep.

Change-Id: I63332dee71a8cd4fdc4b53546ad1e86641dd1a17