Register rule for wallpaper entry

We should keep consistent split rule for wallpaper and other home menu
item. So, we create this cl to register the split rule for wallpaper.

Also, I do some minor refactoring in this cl for reusing existing
method and better code quality.

Test: Go to wallpaper, and click back key. App can close.
Fix: 204406425
Fix: 204364572

Change-Id: Ia7de9483b351d1121cc26c4af1cb8a89ad0a16bc