Merge branch 'Implement-of_get_nvmem_mac_address-helper'

Mike Looijmans says:

====================
of_net: Implement of_get_nvmem_mac_address helper

Posted this as a small set now, with an (optional) second patch that shows
how the changes work and what I've used to test the code on a Topic Miami board.
I've taken the liberty to add appropriate "Acked" and "Review" tags.

v4: Replaced "6" with ETH_ALEN

v3: Add patch that implements mac in nvmem for the Cadence MACB controller
    Remove the integrated of_get_mac_address call

v2: Use of_nvmem_cell_get to avoid needing the assiciated device
    Use void* instead of char*
    Add devicetree binding doc
====================

Signed-off-by: David S. Miller <davem@davemloft.net>