net: bnx2x: fix build error with ptp

bnx2x uses ptp functions, so it should select the provider of
those functions (PTP_1588_CLOCK).  Fixes these build errors:

drivers/built-in.o: In function `__bnx2x_remove':
/home/jim/linux/drivers/net/ethernet/broadcom/bnx2x/bnx2x_main.c:13409:
undefined reference to `ptp_clock_unregister'
drivers/built-in.o: In function `bnx2x_register_phc':
/home/jim/linux/drivers/net/ethernet/broadcom/bnx2x/bnx2x_main.c:13202:
undefined reference to `ptp_clock_register'
drivers/built-in.o: In function `bnx2x_get_ts_info':
/home/jim/linux/drivers/net/ethernet/broadcom/bnx2x/bnx2x_ethtool.c:3498:
undefined reference to `ptp_clock_index'

Reported-by: Jim Davis <jim.epost@gmail.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: David S. Miller <davem@davemloft.net>