Build: split API/ACI checks into separate Makefile targets
    
    This is temporary workaround. makeapi/makeaci transitively import
    ipaplatform, which will not exist before configure is executed.
    On the other hand, configure requires version.m4,
    which is generated by current Makefile.
    
    This change works around this chicked-egg problem. It will disappear
    when we start using top-level configure to generate top-level Makefile.
    
    https://fedorahosted.org/freeipa/ticket/6418
    
    Reviewed-By: Lukas Slebodnik <lslebodn@redhat.com>
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>