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: I367a1d904591b152cb60ee18ae888a1dcad7e129
CRs-Fixed: 806156