tg3 / broadcom: Optionally disable TXC if no link

This patch adds code to disable the TXC and RXC reference clocks if link
is not available.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
3 files changed