net: Introduce a new MII time stamping interface.

Currently the stack supports time stamping in PHY devices.  However,
there are newer, non-PHY devices that can snoop an MII bus and provide
time stamps.  In order to support such devices, this patch introduces
a new interface to be used by both PHY and non-PHY devices.

In addition, the one and only user of the old PHY time stamping API is
converted to the new interface.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>