net/mlx5e: Add HW timestamping (TS) support

Add support for enable/disable HW timestamping for incoming and/or
outgoing packets. To enable/disable HW timestamping appropriate
ioctl should be used. Currently HWTSTAMP_FILTER_ALL/NONE and
HWTSAMP_TX_ON/OFF only are supported. Make all relevant changes in
RX/TX flows to consider TS request and plant HW timestamps into
relevant structures.

Add internal clock for converting hardware timestamp to nanoseconds. In
addition, add a service task to catch internal clock overflow, to make
sure timestamping is accurate.

Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>