net: dsa: microchip: Do not execute PTP driver code for unsupported switches

net: dsa: microchip: Do not execute PTP driver code for unsupported switches

The PTP driver code only works for certain KSZ switches like KSZ9477,
KSZ9567, LAN937X and their varieties.  This code is enabled by kernel
configuration CONFIG_NET_DSA_MICROCHIP_KSZ_PTP.  As the DSA driver is
common to work with all KSZ switches this PTP code is not appropriate
for other unsupported switches.  The ptp_capable indication is added to
the chip data structure to signal whether to execute those code.

Signed-off-by: Tristram Ha <tristram.ha@microchip.com>
Link: https://patch.msgid.link/20241218020240.70601-1-Tristram.Ha@microchip.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>