SystemUI: TabletStatusBar: enable storage notifications

Pulled from CM9 (seems to have been missed in CM10 transition).

Change-Id: Iadaefad05e0aec36c721203de1e382b3c93c9f6e
Merge "SystemUI: TabletStatusBar: enable storage notifications" into jellybean
Merge remote-tracking branch 'upstream/jellybean' into jellybean