GFS2: Clean up ACLs

To prepare for support for caching of ACLs, this cleans up the GFS2
ACL support by pushing the xattr code back into xattr.c and changing
the acl_get function into one which only returns ACLs so that we
can drop the caching function into it shortly.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>