net/faraday: Make EDO{R,T}R bits configurable

These bits are #defined at a fixed location. In order to support future
hardware that has chosen to move these bits around move the bits into a
member of the struct ftgmac100.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: David S. Miller <davem@davemloft.net>