drivers/virtio: Enable virtio mem for ARM64

This enables virtio-mem device support by allowing to enable the
corresponding kernel config option (CONFIG_VIRTIO_MEM) on the
architecture.

Signed-off-by: Gavin Shan <gshan@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://lore.kernel.org/r/20220119010551.181405-1-gshan@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Gavin Shan <gshan@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>