surfaceflinger: Improve dithering method (2/2)

Some devices have blur effect while opening apps.
This fix adds an option(2) for "Fix blur effect".
Dithering is always enabled when persist.sys.use_dithering=2

Change-Id: I5b0b9fd767cd0024f90bbcb952ac53b209151ca7

Conflicts:
	res/xml/performance_settings.xml
	src/com/android/settings/cyanogenmod/PerformanceSettings.java