acpi: add acpi=OnOffAuto machine property to x86 and arm virt

acpi: add acpi=OnOffAuto machine property to x86 and arm virt

Remove the global acpi_enabled bool and replace it with an
acpi OnOffAuto machine property.

qemu throws an error now if you use -no-acpi while the machine
type you are using doesn't support acpi in the first place.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-Id: <20200320100136.11717-1-kraxel@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>