Add device-tree binding documentation for the Tegra210 Audio DMA
controller.
diff --git a/Documentation/devicetree/bindings/dma/tegra210-adma.txt b/Documentation/devicetree/bindings/dma/tegra210-adma.txt
+- #dma-cells : Must be <2>. The first cell denotes the transmit or
+ receive request number and should be between 1 and the maximum number
+ of requests supported (see properties "dma-rx-requests" and
+ "dma-tx-requests"). This value corresponds to the RX/TX_REQUEST_SELECT
+ fields in the ADMA_CHn_CTRL register. The second cell denotes whether
+ the channel is a receive or transmit channel and must be either 2 for
+ a receive channel and 4 for a transmit channel. These values correspond
+ to the TRANSFER_DIRECTION field of the ADMA_CHn_CTRL register.