mfd: tps65217: Set PMIC to shutdown on PWR_EN toggle

Set tps65217 PMIC status to OFF if power enable toggle is supported.
By setting this bit to 1 to enter PMIC to OFF state when PWR_EN pin
is pulled low. Also adds a DT flag to specify that device pmic
supports shutdown control or not.

Signed-off-by: Colin Foe-Parker <colin.foeparker@logicpd.com>
[anilkumar@ti.com: move the additions to tps65217 MFD driver]
Signed-off-by: AnilKumar Ch <anilkumar@ti.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>