realtek: rtl838x: setup SDS entirely in PCS driver

realtek: rtl838x: setup SDS entirely in PCS driver

After having moved the configuration code and sequences from PHY and
DSA drivers to the PCS driver, add the hooks in PCS driver and remove
calls in PHY and DSA drivers to let PCS driver setup the SerDes
entirely on its own.

Also add pcs-handle to device tree definitions for most of the switch
ports because, due to the refactoring of the SerDes configuration, this
is needed now for all SerDes-attached ports.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/20876
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>