soc: qcom: notifier: Put new_server and del_server into workqueue

QMI service use reader thread to call new_server/del_server.
Same thread is used for processing the incoming packets. If
we put the reader thread into sleep use qmi_txn_wait in the
new_server call back, the incoming message will never be
processed, and read thread will not wake up. So use a workqueue
to process the new_server/del_server to free up the read thread.

Change-Id: I23dc5fff232c738b7ebaab403b2c58e3f6e0e1a3
Signed-off-by: Runmin Wang <runminw@codeaurora.org>