Add some missing workarounds in tg3_set_power_state():

1. Workaround to prevent overdrawing current on 5714.

2. Do not power down 5700's PHY because of hw limitation.
Signed-off-by: NMichael Chan <mchan@broadcom.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>