Show "up navigate" icon in input method subtype enabler

Since API 16 (and API 14 with support library) and later, we started
supporting "up navigation" model.
http://developer.android.com/training/implementing-navigation/ancestral.html

As a part of Settings app and a part of an IME's settings activity,
the input method subtype enabler should have a "up navigate icon on
its action bar.

Bug: 16595009
Change-Id: Iaaadd970395b9c9254ab60b2e8fee22dffb8c7f6