net: dsa: microchip: implement get_phy_flags only if needed

net: dsa: microchip: implement get_phy_flags only if needed

The common ksz_get_phy_flags() is used by all the switches to implement
the optional .get_phy_flags DSA operation. It always returns 0 except
for KSZ88X3 switches where an errata has to be handled.

Make ksz_get_phy_flags() ksz88xx-specific.
Remove the get_phy_flags implementation for the switches that don't need
it.

Signed-off-by: Bastien Curutchet (Schneider Electric) <bastien.curutchet@bootlin.com>
Link: https://patch.msgid.link/20260608-clean-ksz-3rd-v2-3-6e61b7be23c4@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>