kvm tools: Add SPAPR PPC64 hcall & rtascall structure

This patch adds the basic structure for HV calls, their registration and some of
the simpler calls.  A similar layout for RTAS calls is also added, again with
some of the simpler RTAS calls used by the guest.  The SPAPR RTAS stub is
generated inline.  Also, nodes for RTAS are added to the device tree.

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>