kernel: add kmod-usb-net-lan78xx

kernel: add kmod-usb-net-lan78xx

Add kernel module for Microchip LAN78XX based USB 2 & USB 3
10/100/1000 Ethernet adapters. [1]

This kernel module is required for the Seeed Studio's Mini Router
based on RPI CM4 [2].

[1] <https://cateee.net/lkddb/web-lkddb/USB_LAN78XX.html>
[2] <https://www.seeedstudio.com/Dual-GbE-Carrier-Board-with-4GB-RAM-32GB-eMMC-RPi-CM4-Case-p-5029.html>

Link: <https://github.com/openwrt/openwrt/pull/4893>
Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
(added kmod-phy-microchip and kmod-fixed-phy dependencies,
rpi3 needs lan78xx but has it built-in)
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>