dt-bindings: net: brcm,amac: Allow "dma-coherent" property

The Broadcom AMAC controller is DMA coherent on some platforms, so allow
the dma-coherent property.

Reviewed-by: Florian Fainelli <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Rob Herring (Arm) <[e-mail]>

Documentation/devicetree/bindings/net/brcm,amac.yaml

···
       - const: idm_base
       - const: nicpm_base
 
+  dma-coherent: true
+
 unevaluatedProperties: false
 
 examples: