Revert "generic: add mac-address property for NVMEM mac addresses"

Revert "generic: add mac-address property for NVMEM mac addresses"

This reverts commit b30924873062be47250e6b872347461c8221688d.

This commit could create a property without allocated memory, breaking
subsequent reads over a nodes property. Also, the mac-address-increment
was not applied when reading from nvmem.

Revert this commit for now, which breaks the label-mac-address logic.
Possibly, traversing the device-tree from the netdev side is easier
anyways.

Signed-off-by: David Bauer <mail@david-bauer.net>