SystemUI: Improve string in data capable, not selected scenario.

  If a user hotswaps out their SIMs on a multisim device, the
  default data sim can be in an "unset" state. Since this is
  a possible scenario, its better to show that no data sim
  is selected vs no sims being available.

Change-Id: I1e077883472a5037f38f97e6d15afe504f787e6a
TICKET: CYNGNOS-2211