ptp: netc: add external trigger stamp support

ptp: netc: add external trigger stamp support

The NETC Timer is capable of recording the timestamp on receipt of an
external pulse on a GPIO pin. It supports two such external triggers.
The recorded value is saved in a 16 entry FIFO accessed by
TMR_ETTSa_H/L. An interrupt can be generated when the trigger occurs,
when the FIFO reaches a threshold or overflows.

Signed-off-by: F.S. Peng <fushi.peng@nxp.com>
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20250829050615.1247468-8-wei.fang@nxp.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>