msm: restart: add support for SPMI PMIC arbiter shutdown

Add a secure monitor call into the V2 restart and shutdown paths
which disables the SPMI PMIC arbiter immediately before the
PS_HOLD signal is lowered to restart or shutdown the target.
This feature is used to avoid PMIC SPMI lockups that occur on
certain PMIC chips if PS_HOLD is lowered in the middle of an
SPMI transaction.

Change-Id: I0d689cb99d6cc04879baa3dea05fa70cf00fb2ef
CRs-Fixed: 517979
Signed-off-by: David Collins <collinsd@codeaurora.org>