docs: Note hvf support for domain elements

docs: Note hvf support for domain elements

Many domain elements have "QEMU and KVM only" or "QEMU/KVM since x.y.z"
remarks. Most of the elements work for HVF domain, so it makes sense to
add respective notices for HVF domain.

All the elements have been manually tested.

Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Tested-by: Brad Laue <brad@brad-x.com>
Tested-by: Christophe Fergeau <cfergeau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>