base-files: rename ethernet devs on known boards

base-files: rename ethernet devs on known boards

Some platforms lack an established way to name netdevs; for example,
on x86, PCIe-based ethernet interfaces will be named starting from
eth0 in the order they are probed. This is a problem for many devices
supported explicitly by OpenWrt which have hard-wired, standalone or
on-CPU NICs not supported by DSA (which is usually used to rename the
ports based on their ostensible function).

To fix this, add a mapping between ethernet device name and sysfs
device path to board.json; this allows us to configure ethernet device
names we know about for a given board so that they correspond to
external labeling.

Signed-off-by: Martin Kennedy <hurricos@gmail.com>