Scroll if an accessibility setting description does not fit the screen.

1. Certain accessibility settings are shown on a separate screen with
   a toggle switch and a description. Sometimes the description does not
   fit the screen. The preference framework is using a list view for
   holding the description item. This list view was disabled, thus not
   scrolling (done to avoid drawable state change on click). Now the
   list view is enabled and the drawable state change on click problem
   is solved by setting the selector and divider drawables to a
   transparent one.

2. The layout for the list item that shows the feature description had
   an unnecessary linear layout.

bug:8632146

Change-Id: Ib81a8513158d5b8d90fa80f57720c8590022ae1a