arm: am335x: Honor pmic option ti,pmic-shutdown-controller

arm: am335x: Honor pmic option ti,pmic-shutdown-controller

Honor ti,pmic-shutdown-controller option in DTS

Tested on stable r359316 @ Sleep mode on custom hw, Power off on BBB and PB

OFF bit [1] in status register control the pmic behaviour when PWR_EN pin
is pulled low.
On most AM335x hardware [beaglebone *] the desired behaviour are in fact
power off due to some hardware designs - read more in the comments around
pmic in sys/gnu/dts/arm/am335x-bone-common.dtsi

This patch let the device-tree decide with ti,pmic-shutdown-controller[2]
the state of off bit in status register.

[1] 8.6.12 table 12 http://www.ti.com/lit/ds/symlink/tps65217.pdf

[2] Documentation/devicetree/bindings/regulator/tps65217.txt

PR:		245159
Submitted by:	Oskar Holmlund <oskar.holmlund@ohdata.se>
MFC after:	2 weeks