ptp: qoriq: convert to use generic interfaces to set loopback mode

ptp: qoriq: convert to use generic interfaces to set loopback mode

Since the generic debugfs interfaces for setting the periodic pulse
signal loopback have been added to the ptp_clock driver, so convert
the vendor-defined debugfs interfaces to the generic interfaces.

Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://patch.msgid.link/20250905030711.1509648-4-wei.fang@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>