PM / hibernate: Fix restore hang in freeze_processes()

PM / hibernate: Fix restore hang in freeze_processes()

During restore, pm_notifier chain are called with
PM_RESTORE_PREPARE.  The firmware_class driver handler
fw_pm_notify does not have a handler for this.  As a result,
it keeps a reader on the kmod.c umhelper_sem.  During
freeze_processes, the call to __usermodehelper_disable tries to
take a write lock on this semaphore and hangs waiting.

Signed-off-by: Sebastian Capella <[email protected]>
Acked-by: Ming Lei <[email protected]>
Cc: All applicable <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>