net: phy: dp83822: Add support for changing the transmit amplitude voltage

net: phy: dp83822: Add support for changing the transmit amplitude voltage

Add support for changing the transmit amplitude voltage in 100BASE-TX mode.
Modifying it can be necessary to compensate losses on the PCB and
connector, so the voltages measured on the RJ45 pins are conforming.

Signed-off-by: Dimitri Fedrau <dimitri.fedrau@liebherr.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250214-dp83822-tx-swing-v5-3-02ca72620599@liebherr.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>