s3:lib/afs move afs.c to common lib dir

some of the code in afs.c is needed by wbinfo that lives in the toplevel
nsswitch directory, so move the afs.c file to a new top-level lib/afs
directory. Use the name afs_funcs to avoid collisions with the afs.h
header from OpenAFS

Signed-off-by: Christian Ambach <ambi@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>