Merge branch 'macb'

From: Soren Brinkmann <soren.brinkmann@xilinx.com>

====================
net: macb updates

I'd really like to have Ethernet working for Zynq, so I want to at least
revive this discussion regarding this patchset. And the first four
patches should not even be too controversial.
I didn't change anything compared to my original RFC submission, except
for a typo in one of the commit messages.
Handling the tx_clk as optional clock input seems a little bit weird,
but it works on my Zynq platform and should be compatible with other
users of macb and their DT descriptions.
====================

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