net: thunderx: add timestamping support

This adds timestamping support for both receive and transmit
paths. On the receive side no filters are supported i.e either
all pkts will get a timestamp appended infront of the packet or none.
On the transmit side HW doesn't support timestamp insertion but
only generates a separate CQE with transmitted packet's timestamp.
Also HW supports only one packet at a time for timestamping on the
transmit side.

Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
Signed-off-by: Aleksey Makarov <aleksey.makarov@cavium.com>
Acked-by: Philippe Ombredanne <pombredanne@nexb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>