net: dsa: microchip: ptp: Initial hardware time stamping support

This patch adds the routine for get_ts_info, hwstamp_get, set. This enables
the PTP support towards userspace applications such as linuxptp.

Signed-off-by: Christian Eggers <ceggers@arri.de>
Co-developed-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>