pkgbase: split kerberos binaries and libs
This allows installing packages that depend on kerberos libraries
without pulling in all the binaries. It also moves libgssapi to runtime
to allow installing kerbereos libraries without adding a dependancy on
the large utilities package. It makes sense to put libgssapi in runtime
rather than kerberos-lib since this is a plugin layer which is intended
to support any GSS-API mechanisms, not just kerberos.
A good example of a package which uses kerberos libraries without
needing the kerberos utilities is sshd. This uses the kerberos GSS-API
libraries to implement its GSSAPIAuthentication option.
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D36028