probe: improve basemac and prodname detection

[troglobit]

Devices like the R2S and VisionFive2 don't have a Base MAC address. If you're lucky, as in the case of the VisionFive2, you may have an EEPROM with unique MAC addresses for the interfaces, but it's unlikely to be in ONIE format. For both the above platforms this causes the hostname to be infix-00-00-00:

root@infix-00-00-00:/>

Both the the Infix defined basemac and prodname should be derived a fallback manner, preferably in a structured/plugin based way of providers of said information.

E.g., if no basemac is available, use the lowest MAC address of the interfaces. Use the device tree name for prodname, etc.

[troglobit]

Base MAC fallback handling added in 4b55e38