esoc: mdm-4x: Always poweroff the modem using AP2M_PON

In case of a shutdown of the modem, even if we see the mdm
initiate a shutdown on its own, we need to explicitly power
off the mdm from APQ end. If the AP2M_PON remains high,
the mdm will power back on.

Change-Id: I9a2e6dc84667005178add3303e0ce399bd54cd61
Signed-off-by: Hanumant Singh <hanumant@codeaurora.org>