20: move doc comments inside macro invocations r=Disasm a=euclio

[rust-lang/rust#57882](https://github.com/rust-lang/rust/pull/57882

) is modifying the `unused_doc_comments` lint to fire on mistakenly documented macro expansions. Note that these doc comments are not currently used, since they are eliminated when the macro is expanded. A crater run detected that this crate will break due to this change, likely because of the use of `deny(unused_doc_comments)` or `deny(warnings)`.

While this kind of breakage is allowed under Rust's stability guarantees, I am opening PRs to affected crates to reduce the impact.

This PR protects your crate from future breakage by moving the offending doc comments inside the macro invocations.

Co-authored-by: Andy Russell <arussell123@gmail.com>

19: Add team e-mail to authors r=dvc94ch a=Disasm



Co-authored-by: Vadim Kaushan <admin@disasm.info>

18: remove the unused 'const-fn' feature r=Disasm a=japaric

note that is technically a breaking change

Co-authored-by: Jorge Aparicio <jorge@japaric.io>

17: Update docs and bump version r=dvc94ch a=Disasm

cc @rust-embedded/riscv

Co-authored-by: Vadim Kaushan <admin@disasm.info>

https://riscv.org/risc-v-trademark-usage/

16: Build on stable r=dvc94ch a=Disasm



Co-authored-by: Vadim Kaushan <admin@disasm.info>

15: Refactoring: use new macros for M-mode CSRs r=dvc94ch a=Disasm



Co-authored-by: Vadim Kaushan <admin@disasm.info>

12: Add some S-Mode CSRs r=dvc94ch a=wangrunji0408

Add these S-Mode CSRs:
- `sstatus`
- `stvec`
- `sie`
- `sip`
- `scause`
- `stval`
- `sscratch`
- `sepc`
- `satp`

as well as:
- `time`
- `timeh`

and S-Mode instructions:
- `sfence.vma`

Most of the code have been tested in the [RustOS](https://github.com/wangrunji0408/RustOS) project.

14: Remove ecall and *ret instructions from riscv::asm r=dvc94ch a=Disasm

* *ret instructions should not be used directly in Rust code, they should be used in handlers, written in asm ([example](https://github.com/rust-embedded/riscv-rt/blob/273f0d4f70418a7602678632dcc78dbe24208fe2/src/lib.rs#L294-L340)

).
* ecall instruction should be wrapped into something like syscall(), which should be declared in another platform-specific crate.

Co-authored-by: WangRunji <wangrunji0408@163.com>
Co-authored-by: Vadim Kaushan <admin@disasm.info>

13: Replace no-op with unimplemented!() r=dvc94ch a=Disasm



Co-authored-by: Vadim Kaushan <admin@disasm.info>

- use macros to simplify CSR ops
- use crate 'bit_field' to make bits operation clear

10: these raw instructions are unsafe r=dvc94ch a=strake

`wfi` is safe, but the rest are not. Let's make them all unsafe until we have a better idea — the return types are wrong anyhow.


Co-authored-by: M Farkas-Dyck <strake888@gmail.com>

9: use `NonZeroUsize` where appropriate r=dvc94ch a=strake



Co-authored-by: M Farkas-Dyck <strake888@gmail.com>

8: mepc is word-size r=dvc94ch a=strake



Co-authored-by: M Farkas-Dyck <strake888@gmail.com>

In the original riscv-rust fork the target arch was simply named
"riscv", but RISC-V support landed in Rust with "riscv32" as the arch
name instead.

Include "riscv64" optimistically for future-proofing.