IMS: Fix CF icon issue when enable from UI.

If call forwarding is enabled, then the call
forwarding icon should be shown in notification
bar irrespective of SIM having EfCfis and EfCff.
Add code to store CF flag in shared preference
and update the status when enable or disable it
via UI settings menu.

Change-Id: I5d5564824d28f166e6761304f2b49cff36b3b551
CRs-Fixed: 806156