lib8390: enable transmit and receive time stamping.

This patch enables software (and phy device) time stamping. This file is
included by drivers/net/ax88796.c, which is based on phylib. So, this
patch makes hardware time stamping in the PHY possible.

Compile tested only.

Signed-off-by: Richard Cochran <richard.cochran@omicron.at>
Signed-off-by: David S. Miller <davem@davemloft.net>