dt-bindings: serial: sprd: Add dma properties to support DMA mode

This patch adds dmas and dma-names properties for the UART DMA mode.
Signed-off-by: Lanqing Liu <lanqing.liu@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/sprd-uart.txt

@@ -15,12 +15,18 @@ Required properties:
   UART clock and source clock are optional properties, but enable clock
   is required.
 
+Optional properties:
+- dma-names: Should contain "rx" for receive and "tx" for transmit channels.
+- dmas: A list of dma specifiers, one for each entry in dma-names.
+
 Example:
 	uart0: serial@0 {
 		compatible = "sprd,sc9860-uart",
 			     "sprd,sc9836-uart";
 		reg = <0x0 0x100>;
 		interrupts = <GIC_SPI 2 IRQ_TYPE_LEVEL_HIGH>;
+		dma-names = "rx", "tx";
+		dmas = <&ap_dma 19>, <&ap_dma 20>;
 		clock-names = "enable", "uart", "source";
 		clocks = <&clk_ap_apb_gates 9>, <&clk_uart0>, <&ext_26m>;
 	};