dt-bindings: net: fsl,fman: allow dma-coherent property

Add dma-coherent property to fix below warning.
arch/arm64/boot/dts/freescale/fsl-ls1046a-rdb.dtb: fman@1a00000: 'dma-coherent', 'ptimer-handle' do not match any of the regexes: '^ethernet@[a-f0-9]+$', '^mdio@[a-f0-9]+$', '^muram@[a-f0-9]+$', '^phc@[a-f0-9]+$', '^port@[a-f0-9]+$', 'pinctrl-[0-9]+'
from schema $id: http://devicetree.org/schemas/net/fsl,fman.yaml#

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

Documentation/devicetree/bindings/net/fsl,fman.yaml

···
       - description: The first element is associated with the event interrupts.
       - description: the second element is associated with the error interrupts.
 
+  dma-coherent: true
+
   fsl,qman-channel-range:
     $ref: /schemas/types.yaml#/definitions/uint32-array
     description: