Enable high-end graphics & fix wallpaper drawing

Let's enable highend graphics by default - it can be disabled by
user preference via Settings -> Performance.

Also set ro.systemui.use_gl_wallpaper=0 to disable opengl wallpaper
rendering (which doesn't work on VideoCoreIV right now).

Change-Id: Ib66a6f0bfbbe1d11143cc0d5e348f9c7a4a6a1e4