dt-bindings: interconnect: Add a dma interconnect name

The current DT bindings assume that the DMA will be performed by the
devices through their parent DT node, and rely on that assumption for the
address translation using dma-ranges.

However, some SoCs have devices that will perform DMA through another bus,
with separate address translation rules. We therefore need to express that
relationship, through the special interconnect name "dma-mem".

Acked-by: Georgi Djakov <georgi.djakov@linaro.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/interconnect/interconnect.txt

@@ -51,6 +51,10 @@ interconnect-names : List of interconnect path name strings sorted in the same
 		     interconnect-names to match interconnect paths with interconnect
 		     specifier pairs.
 
+                     Reserved interconnect names:
+			 * dma-mem: Path from the device to the main memory of
+			            the system
+
 Example:
 
 	sdhci@7864000 {