msm: qpnp-power-on: Store device shut down in PMIC register

Add an option to set a PMIC register for keeping a device
in the shutdown state. If a user initiates a shutdown by pressing the
power key the device will stay OFF instead of initiates a reset.

Change-Id: I531bc63ca42bc01b603e9488f214f22a9d973810
Signed-off-by: Shimrit Malichi <smalichi@codeaurora.org>