bnxt_en: Move bnxt_ptp_init() to bnxt_open()

The device needs to be in ifup state for PTP to function, so move
bnxt_ptp_init() to bnxt_open().  This means that the PHC will be
registered during bnxt_open().

This also makes firmware reset work correctly.  PTP configurations
may change after firmware upgrade or downgrade.  bnxt_open() will
be called after firmware reset, so it will work properly.

bnxt_ptp_start() is now incorporated into bnxt_ptp_init().  We now
also need to call bnxt_ptp_clear() in bnxt_close().

Fixes: 93cb62d9 ("bnxt_en: Enable hardware PTP support")
Cc: Richard Cochran <richardcochran@gmail.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>