virt: move tpm device to vmdevices.py

No real code changes

Change-Id: I43924e71718e833f9ce274e15d89aebe5fea935c
Signed-off-by: Martin Polednik <mpolednik@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/34306
Reviewed-by: Francesco Romani <fromani@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>