net: dsa: lantiq_gswip: support model-specific mac_select_pcs()

net: dsa: lantiq_gswip: support model-specific mac_select_pcs()

Call mac_select_pcs() function if provided in struct gswip_hwinfo.
The MaxLinear GSW1xx series got one port wired to a SerDes PCS and
PHY which can do 1000Base-X, 2500Base-X and SGMII. Support for the
SerDes port will be provided using phylink_pcs, so provide a
convenient way for mac_select_pcs() to differ based on the hardware
model.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Hauke Mehrtens <hauke@hauke-m.de>
Link: https://patch.msgid.link/7668666aa51e43e7f2a6cbcf36eb5a0a3020998f.1756520811.git.daniel@makrotopia.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>