grouper: Better background gradients

Now lots of backgrounds look a bit ugly.
Using another dithering mode produces better gradients

Change-Id: I1907f02cb3c0c96ae7337d9eda17e7b39bf86db7
Merge branch 'cm-10.2' of https://github.com/CyanogenMod/android_kernel_asus_grouper into DJL10.2