net: phy: bcm7xxx: add workaround for PHY revision E0 and F0

PHY revisions E0 and F0 share the same shorter workaround initialization
sequence. Dedicate a special function for these two PHY revisions to
perform the needed workaround sequence.

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