hw/virtio: enable common virtio feature for mmio device

Both 'indirect_desc' and 'event_idx' are bus independent features,
and they should be enabled for mmio devices too.

On arm64 quad core VM(qemu-kvm), the patch can increase block I/O
performance a lot with latest linux tree:
        - without the patch: 14K IOPS
        - with the patch: 34K IOPS

fio script:
        [global]
        direct=1
        bsrange=4k-4k
        timeout=10
        numjobs=4
        ioengine=libaio
        iodepth=64

        filename=/dev/vdc
        group_reporting=1

        [f1]
        rw=randread

Cc: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Acked-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio-mmio.c

@@ -369,10 +369,16 @@ static void virtio_mmio_realizefn(DeviceState *d, Error **errp)
     sysbus_init_mmio(sbd, &proxy->iomem);
 }
 
+static Property virtio_mmio_properties[] = {
+    DEFINE_VIRTIO_COMMON_FEATURES(VirtIOMMIOProxy, host_features),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
 static void virtio_mmio_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
 
+    dc->props = virtio_mmio_properties;
     dc->realize = virtio_mmio_realizefn;
     dc->reset = virtio_mmio_reset;
     set_bit(DEVICE_CATEGORY_MISC, dc->categories);