realtek: pcs: cover number of links per SerDes for USXGMII

realtek: pcs: cover number of links per SerDes for USXGMII

A SerDes may supply multiple ports and depending on that number,
different hardware modes need to be used. While there are corresponding
modes in the kernel in some cases (e.g. USXGMII with 4 2.5G ports aka
10G-QXGMII), this doesn't always map to Realtek hardware modes. Use the
previously added link number accounting for that.

An obvious example of this is the SerDes on XGS12xx-12 switches which
is connected to an octa-PHY. This runs Realtek proprietary XSGMII mode
(10G-pumped SGMII interface) for which there is no corresponding mode
in the kernel.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21365
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>