power: qpnp-fg: stop IMA transactions during FG shutdown

There is a chance that IMA transactions can happen when the
system goes for a reset. This can cause problems especially if
it is a warm reset. To avoid this, make sure that no IMA
transactions happen when the system goes for a reset.

CRs-Fixed: 962694
Change-Id: I48b0229150f13b2ae05c46b4583c4a4900b72b0b
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>