dt-bindings: dma: fsl,imx-dma: Document the DMA clocks

Document the IPG and AHB clocks that are needed by the DMA hardware
as required properties.

It is not possible to have DMA functional without the DMA clocks
being turned on.

Signed-off-by: Fabio Estevam <[e-mail]>
Acked-by: Conor Dooley <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

Documentation/devicetree/bindings/dma/fsl,imx-dma.yaml

···
       - description: DMA Error interrupt
     minItems: 1
 
+  clocks:
+    maxItems: 2
+
+  clock-names:
+    items:
+      - const: ipg
+      - const: ahb
+
   "#dma-cells":
     const: 1
 
···
   - reg
   - interrupts
   - "#dma-cells"
+  - clocks
+  - clock-names
 
 additionalProperties: false
 
 examples:
   - |
+    #include <dt-bindings/clock/imx27-clock.h>
+
     dma-controller@10001000 {
       compatible = "fsl,imx27-dma";
       reg = <0x10001000 0x1000>;
       interrupts = <32 33>;
       #dma-cells = <1>;
       dma-channels = <16>;
+      clocks = <&clks IMX27_CLK_DMA_IPG_GATE>, <&clks IMX27_CLK_DMA_AHB_GATE>;
+      clock-names = "ipg", "ahb";
     };