EAP-AKA': Allow both AKA AKA' to be registed from eap_aka_prime.c

EAP-AKA': Allow both AKA AKA' to be registed from eap_aka_prime.c

This allows the same source code file to be shared for both methods. For
now, this is only in eap_aka_prime.c, but eventually, changes in
eap_aka_prime.c are likely to be merged into eap_aka.c at which point
the separate eap_aka_prime.c can be removed.