Fix uneven spacing of navigation bar buttons in landscape

* Add two dummy views to the left and right corners to
  bring the buttons nearer to the center
* This makes it easier to hit the back and recents key,
  and makes it identical to what the Sony firmware has.

Same as commit 'd2af20ff1077b2edbc85160dde94db809dbf3643',
but for landscape

Change-Id: Ib4c531d587e56db8878b00a5bd2e2a738692b622
overlay: SystemUI: add left and right virtual buttons while typing

Change-Id: Iea446443d33ff305765e47c86523b619676116ac