rust: usb: porting usbsevseg.c to Rust

[alexandruradovici]

The main purpose of this is to add USB data transfer abstractions. This is more of a tracking issue.

To have an example driver ported to Rust, I chose usbsevseg.c, as it is rather simple and involves only control transfers for now. The steps would be:

• add endpoint discovery - PATCH v2 1/4
• add control transfers - PATCH v2 2/4
• add sysfs abstractions (as usbsevseg.c uses sysfs) - PATCH v2 3/4
• add sysfs to USB - PATCH v2 4/4
• port the driver

I have sent the patches to the kernel list, I would really appreciate some feedback around it, mostly for sysfs. I already had a very good conversation with Greg over v1.

I am having a Kernel Workshop at RustConf where I will use the patch and get additional feedback, but any suggestion of polish until then is very welcome.

Thank you.