soc: qcom: sysmon: Use singlethread workqueue for QMI notif callbacks

Currently, by using the shared workqueue, there is no guarantee
that the SERVICE_ARRIVE notification callback will be executed
by the time that the SERVICE_EXIT notification callback is
triggered if the service up/down happens almost instantaneously.
Use a singlethread workqueue to fix this condition.

Change-Id: I57cff7885d64460e80581d98800fee34dd496262
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>