kvm tools: Add SPAPR PPC64 HV console

This adds the console code, plus VIO HV terminal nodes are added to
the device tree so the guest kernel will pick it up.

Signed-off-by: Matt Evans <matt@ozlabs.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Pekka Enberg <penberg@kernel.org>