Merge branch 'net-dsa-mxl862xx-serdes-ports'

Daniel Golle says:

====================
net: dsa: mxl862xx: SerDes ports

Add support for the two SerDes PCS interfaces of the MxL862xx switch
ICs, which can both either be used to connect PHYs or SFP cages, or as
CPU port(s). 1000Base-X, 2500Base-X, 10GBase-R, 10GBase-KR, SGMII,
QSGMII and USXGMII (single 10G or quad 2.5G) are supported.

The firmware only added the API to directly control the PCS as of
version 1.0.84, so the PCS features are gated behind a version check.

As the driver is growing do some refactoring to break out the phylink
parts into mxl862xx-phylink.h.
====================

Link: https://patch.msgid.link/cover.1781319534.git.daniel@makrotopia.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>