Fix XMega information for wizard.

The wizard did not generate a working set of makefiles, I
needed to add "xmega" to CPU_TAGS. While doing this I decided to create
a xmega.common file with these xmega specific settings and include it
from ATxmega32D4.cdef.

Signed-off-by: Onno <developer@gorgoz.org>
git-svn-id: https://src.develer.com/svnoss/bertos/trunk@5162 38d2e660-2303-0410-9eaa-f027e97ec537