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

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

Change-Id: Ibfac397bf38749b095dacab4cadf7b77bd003e88
Signed-off-by: Avaneesh Kumar Dwivedi <akdwived@codeaurora.org>