realtek: pcs: rtl930x: drop conditional SerDes setup

realtek: pcs: rtl930x: drop conditional SerDes setup

We can now setup most of the modes for RTL930x, recently XSGMII, QSGMII
and USXGMII-SX have been added. Thus we don't need a big list of allowed
modes anymore in SerDes setup. Drop this without replacement. Other
modes are still rejected in other places or will be rejected later with
a proper SerDes capability handling.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21930
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>