net: dsa: microchip: ptp: lan937x: add 2 step timestamping

LAN937x series of switches support 2 step timestamping mechanism. There
are timestamp correction calculation performed in ksz_rcv_timestamp and
ksz_xmit_timestamp which are applicable only for p2p1step. To check
whether the 2 step is enabled or not in tag_ksz.c introduced the helper
function in taggger_data to query it from ksz_ptp.c. Based on whether 2
step is enabled or not, timestamp calculation are performed.

Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>