[TG3]: add 5780 fiber support

Add 5780S support by adding a new tg3_setup_fiber_mii_phy() function and
a timer function for parallel link detection. 5780S uses standard MII
registers for 1000BaseX and runs in GMII mode as opposed to TBI mode on
older serdes chips.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>