dt-bindings: net: ethernet-phy: add property mac-termination-ohms

Add property mac-termination-ohms in the device tree bindings for selecting
the resistance value of the builtin series termination resistors of the
PHY. Changing the resistance to an appropriate value can reduce signal
reflections and therefore improve signal quality.

Signed-off-by: Dimitri Fedrau <dimitri.fedrau@liebherr.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20250416-dp83822-mac-impedance-v3-1-028ac426cddb@liebherr.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>