Use enums for machine constants

[Oshgnacknak]

It might make sense to use enums at

control/machines/src/lib.rs

Line 33 in 1406d6c

pub const VENDOR_QITECH: u16 = 0x0001;

and following lines.

One can make enum constants equal to const values and automatically get an into() method.

#[repr(u16)]
enum MyEnum {
    Qitech = 1,
    Other = 2
}
const x: u16 = MyEnum::Qitech.into();