Merge branch 'net-dsa-mxl-gsw1xx-setup-polarities-and-validate-chip'

Daniel Golle says:

====================
net: dsa: mxl-gsw1xx: setup polarities and validate chip

Now that common PHY properties make it easy to configure the SerDes RX
and TX polarities, use that for the SGMII/1000Base-X/2500Base-X port of
the MaxLinear GSW1xx switches.

Also, validate hardware in probe() function to make sure the switch is
actually present and MDIO communication works properly.
====================

Link: https://patch.msgid.link/cover.1769916962.git.daniel@makrotopia.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>