Rust ENC28J60 ethernet driver working on Raspberry Pi

[Ryo Munakata <ryomnktml@gmail.com>]

Hi all,

I've written an ethernet driver for ENC28J60, a stand-alone ethernet 
controller with a SPI interface, in Rust.
It works fine on Raspberry Pi 4B with Raspbian AArch64.
You can connect to the internet and play some videos on YouTube with it 
(10BASE-T though).
I hope it will be an example of real-world drivers in Rust.

* ENC28J60 ethernet driver in Rust
enc28j60rs: https://github.com/pfpacket/enc28j60rs
`impl Sync/Send`, mostly because of raw pointers, and the initialization 
of `workqueue::Work` and `sync::Spinlock`
require a tiny bit of "unsafe" code, but otherwise no unsafe code used.

* The forked kernel with Rust support for SPI and netdev
https://github.com/pfpacket/linux-rpi-rust/tree/rust-netdev
Forked from the Raspberry Pi tree and merged Rust-for-Linux `rust` 
branch into it.
(BTW are there any easier way to get Rust-for-Linux work on Raspberry 
Pi? If so please let me know.)
Then I added the SPI support referencing rust/kernel/platform.rs and 
netdev support.
The netdev support is based on the following GitHub PR from Fujita-san:
https://github.com/Rust-for-Linux/linux/pull/908

Regards,
Ryo Munakata