net: macb: Enable PTP unicast

Enable transmission and reception of PTP unicast packets by
updating PTP unicast config bit and setting current HW mac
address as allowed address in PTP unicast filter registers.

Signed-off-by: Harini Katakam <harini.katakam@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>