net: macb: TSU clock and PTP fixes

Enable transmission and reception of PTP unicast packets.
Add tsu_clk and get the rate for the same from clock framework.
Move definition of tsu_rate to be in sync with master.
Add spinlocks in ptp_remove to avoid issues during suspend/resume.

Signed-off-by: Harini Katakam <harini.katakam@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>