ARM: dts: qcom: add mode control for S8C regulator for SM8150

PMIC PM8150A SMPS regulator S8C is a parent of several LDO
regulators.  Barring an application processor mode request, the
S8C 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 S8C so that application processor
consumers can vote to keep S8C in AUTO mode when needed.  This
avoids power faults during AOSS sleep.

Change-Id: Ie76981cdd1c757f1e40375df4c38d735da2b1be5
Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>