tg3: Disable 5717 serdes and B0 support

The B0 revision of the 5717 will not get enough testing by the time
2.6.33 ships.  Since the kernel is already at RC3, serdes support
will require too many patches to fix.  For these reasons, this patch
disables 5717 serdes support and will refuse to attach to all 5717
devices that are later than an A0 revision.

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