dt-bindings: net: add schema for ASIX USB Ethernet controllers

Create schema for ASIX USB Ethernet controllers and import some of
currently supported USB IDs form drivers/net/usb/asix_devices.c

These devices are already used in some of DTs. So, this schema makes it official.
NOTE: there was no previously documented txt based DT binding for this
controllers.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220517111505.929722-2-o.rempel@pengutronix.de