bnxt_en: Handle async event when the PHC is updated in RTC mode

In Multi-host environment, when the PHC is updated by one host,
an async message from firmware will be sent to other hosts.
Re-initialize the timecounter when the driver receives this
async message.

Cc: Richard Cochran <richardcochran@gmail.com>
Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>
Signed-off-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>