virt 3.0 now allows up to 512 vcpus whereas for earlier machine
types, max_cpus was set to 255 and any attempt to start the
machine with vcpus > 255 was rejected at a very early stage,
in vl.c/main level.

512 is the max supported by KVM. Anyway the actual vcpu count
that can be achieved depends on other parameters such as the
acceleration mode, the vgic version, the host kernel version.
Those are discovered later on.
Signed-off-by: NEric Auger <eric.auger@redhat.com>
Reviewed-by: NAndrew Jones <drjones@redhat.com>
Message-id: 1529072910-16156-12-git-send-email-eric.auger@redhat.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>