virtio: mmio: Allow instantiation via platform data

The m68k QEMU virt machine doesn't use devicetree, yet, so
allow it to create virtio-mmio instances via platform data.

Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Reviewed-by: Angelo Dureghello <angelo@kernel-space.org>
Signed-off-by: Daniel Palmer <daniel@thingy.jp>

include/virtio_mmio.h

@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+
+#ifndef __VIRTIO_MMIO_H__
+#define __VIRTIO_MMIO_H__
+
+#include <linux/types.h>
+
+struct virtio_mmio_plat {
+	phys_addr_t base;
+};
+
+#endif /* __VIRTIO_MMIO_H__ */