dt-bindings: serial: samsung: add DMA properties

The Samsung SoC UART nodes have usually DMA so dtschema has to reflect
this to fix dtbs_check warnings like:

  arch/arm/boot/dts/exynos4210-smdkv310.dt.yaml: serial@13800000:
    'dma-names', 'dmas' do not match any of the regexes: 'pinctrl-[0-9]+'

Signed-off-by: Krzysztof Kozlowski <[email protected]>
Reviewed-by: Rob Herring <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Documentation/devicetree/bindings/serial/samsung_uart.yaml

@@ -52,6 +52,16 @@ properties:
       - pattern: '^clk_uart_baud[0-3]$'
       - pattern: '^clk_uart_baud[0-3]$'
 
+  dmas:
+    items:
+      - description: DMA controller phandle and request line for RX
+      - description: DMA controller phandle and request line for TX
+
+  dma-names:
+    items:
+      - const: rx
+      - const: tx
+
   interrupts:
     description: RX interrupt and optionally TX interrupt.
     minItems: 1