KVM: ia64: add support for Tukwila processors

In Tukwila processor, VT-i has been enhanced in its
implementation, it is often called VT-i2 techonology.
With VTi-2 support, virtulization performance should be
improved. In this patch, we added the related stuff to
support kvm/ia64 for Tukwila processors.

Signed-off-by: Xiantao Zhang <xiantao.zhang@intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>