documentation: dt: bindings: cpsw: fixing the examples for directly using it in dts file

Fixing the cpsw device tree example to make it simpler to copy pastable to dts
file and use it directly.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>