tg3: move init/deinit from open/close to probe/remove

Move init and deinit of PTP support from open/close functions
to probe/remove funcs to avoid removing/re-adding of associated PTP
device(s) during ifup/ifdown.

v2: tg3_ptp_init call moved to correct place (thx. Prashant)

Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Acked-by: Prashant Sreedharan <prashant@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>