dt-bindings: net: Introduce the ethernet-connector description

dt-bindings: net: Introduce the ethernet-connector description

The ability to describe the physical ports of Ethernet devices is useful
to describe multi-port devices, as well as to remove any ambiguity with
regard to the nature of the port.

Moreover, describing ports allows for a better description of features
that are tied to connectors, such as PoE through the PSE-PD devices.

Introduce a binding to allow describing the ports, for now with 2
attributes :

 - The number of pairs, which is a quite generic property that allows
   differentating between multiple similar technologies such as BaseT1
   and "regular" BaseT (which usually means BaseT4).

 - The media that can be used on that port, such as BaseT for Twisted
   Copper, BaseC for coax copper, BaseS/L for Fiber, BaseK for backplane
   ethernet, etc. This allows defining the nature of the port, and
   therefore avoids the need for vendor-specific properties such as
   "micrel,fiber-mode" or "ti,fiber-mode".

The port description lives in its own file, as it is intended in the
future to allow describing the ports for phy-less devices.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20260108080041.553250-2-maxime.chevallier@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>