hw/isa/piix3: Resolve redundant TYPE_PIIX3_XEN_DEVICE

hw/isa/piix3: Resolve redundant TYPE_PIIX3_XEN_DEVICE

During the last patches, TYPE_PIIX3_XEN_DEVICE turned into a clone of
TYPE_PIIX3_DEVICE. Remove this redundancy.

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Tested-by: Chuck Zmudzinski <brchuckz@aol.com>
Message-Id: <20230312120221.99183-7-shentey@gmail.com>
Message-Id: <20230403074124.3925-8-shentey@gmail.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>