SystemUI: Make percentage appear for hidden batt

This commit makes the battery percentage appear in QS when the user
chooses the "hidden battery" option as the battery style. Prior to
this commit, the same battery style was used for the QS tile just
without the percentage indicator. This means no major changes are
being introduced but the usability is being improved as the user
can glance at the QS tile to see the exact percentage instead of
being forced to open the linked Settings page.

Fixes AOSPA-687.

Change-Id: I2131332f2639721f99e149d3add0eb2877b4debe