spec: Advertise nvram paths of official fedora edk2 builds
    
    Fedora now ships edk2 firmware in its official repos, so adapt
    the nvram path list to match. Eventually we can remove the nightly
    links as well once some integration kinks have been worked out,
    and documentation updated.
    
    Move the macro building into the %build target, which lets us
    build up a shell variable and make things a bit more readable
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1335395