msm: subsystem_restart: Ignore SSR requests during system reboot/shutdown

When a system reboot or shutdown is already underway, ignore
SSR errors so that the reboot/shutdown process is uninterrupted.
However, log the SSR request so that we know that the subsystem
behaved unexpectedly.

(cherry picked from commit 3d58c2f7db89ab01f76e7733922408c5a398d465)

Change-Id: I60387a63dcb728e271cf4a512c6546b3d4bce0c3
CRs-Fixed: 416175
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>