frameworks: base: systemui: modify hdpi & xhdpi drawables for battery_min

* These drawables are to large for the new phablet ui. See screenshot:
  http://i.imgur.com/AR8BUH8.png This change modifies the hdpi and xhdpi
  drawables to the sw720p-mdpi drawables, which look correct in the status
  bar.

Patch Set 4: modify commit message to reflect the change

Change-Id: I4f94dbdd37d0b8d9a7efbe9a78c3816eaa33b173