kvm tools: Generate SPAPR PPC64 guest device tree

The generated DT is the bare minimum structure required for SPAPR (on which
subsequent patches for VIO, XICS, PCI etc. will build); root node, cpus, memory.

The DT contains CPU-specific configuration; a very simple 'cpu info' mechanism
is added to recognise/differentiate DT entries for POWER7 and PPC970 host CPUs.
Future support of more CPUs is possible.

libfdt is included from scripts/dtc/libfdt.

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>