pv-qemu 1/10: Add a QEMU machine type for fullvirt guests

pv-qemu 1/10: Add a QEMU machine type for fullvirt guests

This patch does a (no functional change) re-arrangement of the code
for starting up a fully virtualized guest. In particular it creates a
new QEMU machine type for Xen fullyvirt guests which can be specified
with '-M xenfv'. For compatibility this is in fact made to be the
default. The code for setting up memory maps is moved out of vl.c, and
into hw/xen_machine_fv.c. This is basically to ensure that it can be
easily skipped when we add a paravirt machine type in the next patch.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>