gsm/statusbar: Correct CarrierLabel display logic

What's wrong:

* "(No service)|SPN" is shown on lockscreen/statusbar.
* The "(No service)" string won't update on locale change.

What's changed:

statusbar:

* As per lockscreen, the "(No service)" string should be shown only when
  showPlmn is true, and plmn is null.

gsm:

* Run updateSpnDisplay() when ServiceState has not changed (equals() is
  true), but has deregistered (getState() values are different).

* When plmn is null (no service):
 - Set the display rule to show plmn only.
 - Allow updateSpnDisplay() to send the intent on locale change.

Change-Id: Ieab5c93a560c7fbe6a69e2db151d840a30fdbeb4