realtek: pcs: rtl838x: merge and simplify patching

realtek: pcs: rtl838x: merge and simplify patching

Reduce the per-SerDes patching to a per-mode patching since they share a
lot of similarities, especially for QSGMII.

For fiber patching, the differences are bigger. This takes an approach
to merge the sequences completely despite applying some settings which
weren't applied before on one of the SerDes. Testing and SerDes dumps
showed no or minimal differences, and no practical effect on
functionality. A look at the SerDes register documentation we have shows
reordering the writes isn't problematic because most of the bits aren't
any trigger bits.

With all its users gone, we can now drop also the workaround SDS macro.

Link: https://github.com/openwrt/openwrt/pull/23741
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>