Build libafscp when we lack kerberos

Build libafscp when we lack kerberos

Currently, venus fails to build without kerberos, since the
dependencies for afsio always include afscp.h, which does not exist
when we do not build libafscp. To fix this the easy way, and since
libafscp is still very useful without kerberos, allow libafscp to
build without kerberos support (which limits it to anonymous
connections only).

Change-Id: Ief620ca99223f195795dcbe746b47fcbfa2e7450
Reviewed-on: http://gerrit.openafs.org/4577
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>