SystemUI: Follow CM changes for system bars [PS3]

Tracking http://review.cyanogenmod.org/69166
For initial change ID Ibe579d16ea35ca5bdcfe9f98143c3f91cd24900f

This commit removes some hardcoded values and cleans up special casing
as suggested by people in CM. This shouldn't really change anything
for the end user or the theme creator. This only makes the codebase
easier to maintain and understand later down the line.

Change-Id: I8c70e2f1ab7ac789d8beb21a4e8ae7f32db9f015