dma: ste_dma40: Expand DT binding to accept 'high-priority channel' flag

This is used for MSP (audio) devices which is about to be fully DT:ed.

Cc: [e-mail]
Acked-by: Vinod Koul <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

Documentation/devicetree/bindings/dma/ste-dma40.txt

···
         0x00000008: Use fixed channel:
                 Use automatic channel selection when unset
                 Use DMA request line number when set
+        0x00000010: Set channel as high priority:
+                Normal priority when unset
+                High priority when set
 
 Example: