net: phy: bcm7xxx: add PHY revision D0 workaround sequence

PHY revision D0 requires a specific workaround sequence which needs to
be applied to get the HW to behave properly in all corner cases
conditions. Do this based on the revision we just read out of the HW
using a specific function.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>