arch: Make i386 map to i686 instead of athlon
    
    This is used for mapping basearch to binary arch.
    
    One use for this is when running depsolving to tell yum/dnf what arch to
    work with. With this change it will get i686 instead of athlon when
    working on i386 basearch.
    
    The other use case is finding arches compatible with given basearch. The
    change will remove athlon from the list for i386.
    
    Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>