net: dsa: mxl-gsw1xx: configure SerDes port polarities

net: dsa: mxl-gsw1xx: configure SerDes port polarities

Configure SerDes (port 4) RX and TX polarities using the newly
introduced generic properties. The polarities are described at the port
level which equals the polarities of the external pins of the chip.

Note that the RX lane is inverted internally and the vendor driver
simply always sets bit GSW1XX_SGMII_PHY_RX0_CFG2_INVERT unconditionally
to end up with the correct (ie. as documented in datasheets) polarity at
the external pins.

In this sense, PHY_POLARITY_NORMAL denotes normal polarity for pins as
documented for the MRQFN 105-pin package (GSW120, GSW125, GSW140, GSW141
and GSW145 all use the same package and have identical pin layouts
except for TP port 2 and 3 being N/C on GSW12x):
pin B18 (TX0_P) positive signal of the differential SGMII data output pair
pin B19 (TX0_M) negative signal of the differential SGMII data output pair
pin B20 (RX0_P) positive signal of the differential SGMII data input pair
pin B21 (RX0_M) negative signal of the differential SGMII data input pair

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Link: https://patch.msgid.link/8bf79b3476e23673fceffbe2bc9d6abc13d132e5.1769916962.git.daniel@makrotopia.org
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>