device: some Doxygen fixes/improvements

- Align to 80cols
- Fix some incorrect `@p` usages
- Use `@ref foo` to let Doxygen generate references to structs instead
  of using <tt>...</tt>
- Use `@ref struct.field` to reference struct fields
- Use Markdown notation for literals
- use func_name()/MACRO_NAME() to let Doxygen generate references
  automatically without `@ref`
- Fix some minor typos/formatting issues

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>