net: phy: broadcom: support new device flag for setting master mode

Some of Broadcom's PHYs run by default in slave mode with Automatic
Slave/Master configuration disabled. It stops them from working properly
with some devices.

So far it has been verified for BCM54210E and BCM50212E which don't
work well with Intel's I217-LM and I218-LM:
http://ark.intel.com/products/60019/Intel-Ethernet-Connection-I217-LM
http://ark.intel.com/products/71307/Intel-Ethernet-Connection-I218-LM


I was told there is massive ping loss.

This commit adds support for a new flag which can be set by an ethernet
driver to fixup PHY setup.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>