net: ethernet: ti: cpts: move tx timestamp processing to ptp worker only

Now the tx timestamp processing happens from different contexts - softirq
and thread/PTP worker. Enabling IRQ will add one more hard_irq context.
This makes over all defered TX timestamp processing and locking
overcomplicated. Move tx timestamp processing to PTP worker always instead.

napi_rx->cpts_tx_timestamp
 if ptp_packet then
    push to txq
    ptp_schedule_worker()

do_aux_work->cpts_overflow_check
 cpts_process_events()

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>