lantiq: drop duplicate and now unused "lantiq, eth-mac" binding

lantiq: drop duplicate and now unused "lantiq, eth-mac" binding

The device tree binding and the associated code duplicates functionality
already patched into the etop driver. The compatible string isn't used
any more. Therefore the whole code can be dropped.

The "mac-increment" property allowed to increment a mac address received
via kernel cmdline. This functionality isn't used by any device and
should be added as etop driver device tree property if required again.

Signed-off-by: Mathias Kresin <dev@kresin.me>