dt-bindings: virtio_mmio: Add swiotlb device

Add swiotlb node which indicates the memory to be used for
bounding buffers by swiotlb driver.

Change-Id: I3de8df635e8d664928e2bee4476c186323cfe23a

bindings/virtio/swiotlb.yaml

@@ -0,0 +1,31 @@
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/haven/swiotlb.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: SWIOTLB device
+
+description: |+
+  Configuration properties for swiotlb device. This device
+  represents memory that needs to be used for bouncing
+  buffers. The memory typically represents area that is shared
+  with another guest OS.
+
+properties:
+  reg: true
+  dma_base:
+    $ref: '/schemas/types.yaml#/definitions/uint64'
+    description:
+      Constant offset that is added to the DMA address returned by
+      swiotlb_map() API.
+
+required:
+  - reg
+  - dma_base
+
+example:
+  - |
+    swiotlb {
+	reg = <0x0 0xdff00000 0x0 100000>;
+	dma_base = <0x0>;
+    };