Merge branch 'ptp-add-pulse-signal-loopback-support-for-debugging'

Wei Fang says:

====================
ptp: add pulse signal loopback support for debugging

Some PTP devices support looping back the periodic pulse signal for
debugging. For example, the PTP device of QorIQ platform and the NETC v4
Timer has the ability to loop back the pulse signal and record the extts
events for the loopback signal. So we can make sure that the pulse
intervals and their phase alignment are correct from the perspective of
the emitting PHC's time base. In addition, we can use this loopback
feature as a built-in extts event generator when we have no external
equipment which does that. Therefore, add the generic debugfs interfaces
to the ptp_clock driver. The first two patch are separated from the
previous patch set [1]. The third patch is new added.

[1]: https://lore.kernel.org/imx/20250827063332.1217664-1-wei.fang@nxp.com/ #patch 3 and 9
====================

Link: https://patch.msgid.link/20250905030711.1509648-1-wei.fang@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>