Fix the carrier text font size in Keyguard status bar.

Currently the change to display font size wont have the effect
on the carrier text font size in  the Keyguard. Add the text size
which uses sp in keyguard_carrier_text_view.xml.
Add method in CarrierText to handle the Configuration change.

Change-Id: If48a820f534bfb4575973b990bef3ff8e33bf949
CRs-Fixed: 761601.