FIX: Garmin charsets - can display cyrillic maps now.

FIX: Garmin charsets - can display cyrillic maps now.
Register the driver as utf-8 and do the
conversion depending on the actual charset in the map.
gmapsupp.img is a container that can hold several maps combined
and they can have different encodings. But they are registered
as single map in the core. The correct way to do this is
to allow map drivers to register maps in the core.

git-svn-id: https://navit.svn.sourceforge.net/svnroot/navit/trunk@1444 ffa7fe5e-494d-0410-b361-a75ebd5db220