HYPERV isn't available on all architectures, but just on by default
for i386/amd64. Rather, it only works on i386/amd64 and should only be
built there. Rather than change the default based on which
architecutre, do things more directly by only building it on
i386/amd64 and having it always on. This is how we handle other
options that are relevant only for a few architectures.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273155 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f