net: stmmac: Introduce dwmac1000 ptp_clock_info and operations

net: stmmac: Introduce dwmac1000 ptp_clock_info and operations

The PTP configuration for GMAC3_X differs from the other implementations
in several ways :

 - There's only one external snapshot trigger
 - The snapshot configuration is done through the PTP_TCR register,
   whereas the other dwmac variants have a dedicated ACR (auxiliary
   control reg) for that purpose
 - The layout for the PTP_TCR register also differs, as bits 24/25 are
   used for the snapshot configuration. These bits are reserved on other
   variants.

On GMAC3_X, we also can't discover the number of snapshot triggers
automatically.

The GMAC3_X has one PPS output, however it's configuration isn't
supported yet so report 0 n_per_out for now.

Introduce a dedicated set of ptp_clock_info ops and configuration
parameters to reflect these differences specific to GMAC3_X.

This was tested on dwmac_socfpga.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20241112170658.2388529-5-maxime.chevallier@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>