dt-bindings: net: xlnx,axi-ethernet: convert bindings document to yaml

Convert the bindings document for Xilinx AXI Ethernet Subsystem
from txt to yaml. No changes to existing binding description.

Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Signed-off-by: Sarath Babu Naidu Gaddam <sarath.babu.naidu.gaddam@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>