kernel: add Microchip ENC28J60 SPI Ethernet controller module

kernel: add Microchip ENC28J60 SPI Ethernet controller module

The ENC28J60 is a 10 Mbps half-duplex Ethernet controller interfaced via SPI.
It achieves real-world bandwidth up to 5Mbit/s on devices like the RPi Zero due
to SPI limits.
Commonly used with Raspberry Pi Zero boards for wired network connectivity.

Signed-off-by: Albrecht Lohofener <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/19048
Signed-off-by: Álvaro Fernández Rojas <[email protected]>
(cherry picked from commit 4987239913794811b8ac71ff141129e276565d6b)