virtio-mmio: Remove user_creatable flag

virtio-mmio needs to be wired and mapped by other device or board
code, and won't work with -device. Remove the user_creatable flag
from the device class.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Marcel Apfelbaum <marcel@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Shannon Zhao <zhaoshenglong@huawei.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Reviewed-by: NLaszlo Ersek <lersek@redhat.com>
Acked-by: NMarcel Apfelbaum <marcel@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170503203604.31462-20-ehabkost@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

hw/virtio/virtio-mmio.c

@@ -450,11 +450,6 @@ static void virtio_mmio_class_init(ObjectClass *klass, void *data)
     dc->reset = virtio_mmio_reset;
     set_bit(DEVICE_CATEGORY_MISC, dc->categories);
     dc->props = virtio_mmio_properties;
-    /*
-     * FIXME: Set only because we are not sure yet if this device
-     * will be outside the q35 sysbus whitelist.
-     */
-    dc->user_creatable = true;
 }
 
 static const TypeInfo virtio_mmio_info = {