The property use-bcm-hdr was documented as an entry under the ports node
for the bcm_sf2 DSA switch. This property is actually evaluated for each
port. Correct the documentation to match the actual behavior and properly
reference dsa-port.yaml for additional properties of the node.
Suggested-by: Rob Herring <robh@xxxxxxxxxx>
Signed-off-by: Colin Foster <colin.foster@xxxxxxxxxxxxxxxx>