Power off routines for the TWL6030

I've added the power off routines for the TWL6030 chip found on the Duovero. The same Kconfig will do for both the 4030 and the 6030 as the code *should* distinguish between the two chipsets. This has been tested on the Duovero/Parlor combo and verified from a piece of TI code I found later by Rajeev Kulkarni.