dt-bindings: net: cdns,macb: Add versal compatible string

Add versal compatible string.

Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Signed-off-by: Harini Katakam <harini.katakam@xilinx.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>