Hi everyone,
Have spent most of the day working on this one, and have found the following:-
Pine64A+, built the image (Pine64), All is working well, including ethernet in U-Boot.
Pine64-R18, built the image (Pine64so), The image works well, ethernet works in the kernel, however, ethernet was not available via U-Boot (Which is what is required by me).
I compared the device tree configurations within U-Boot between the boards, found the difference between them regarding ethernet configuration and applied the follow patch which then enabled ethernet in U-B