Auto merge of #116485 - coastalwhite:stabilize-riscv-target-features, r=Amanieu

Stabilize Ratified RISC-V Target Features

Stabilization PR for the ratified RISC-V target features. This stabilizes some of the target features tracked by #44839. This is also a part of #114544 and eventually needed for the RISC-V part of rust-lang/rfcs#3268.

There is a similar PR for the the stdarch crate which can be found at rust-lang/stdarch#1476.

This was briefly discussed on Zulip
(https://rust-lang.zulipchat.com/#narrow/stream/250483-t-compiler.2Frisc-v/topic/Stabilization.20of.20RISC-V.20Target.20Features/near/394793704).

Specifically, this PR stabilizes the:
* Atomic Instructions (A) on v2.0
* Compressed Instructions (C) on v2.0
* ~Double-Precision Floating-Point (D) on v2.2~
* ~Embedded Base (E) (Given as `RV32E` / `RV64E`) on v2.0~
* ~Single-Precision Floating-Point (F) on v2.2~
* Integer Multiplication and Division (M) on v2.0
* ~Vector Operations (V) on v1.0~
* Bit Manipulations (B) on v1.0 listed as `zba`, `zbc`, `zbs`
* Scalar Cryptography (Zk) v1.0.1 listed as `zk`, `zkn`, `zknd`, `zkne`, `zknh`, `zkr`, `zks`, `zksed`, `zksh`, `zkt`, `zbkb`, `zbkc` `zkbx`
* ~Double-Precision Floating-Point in Integer Register (Zdinx) on v1.0~
* ~Half-Precision Floating-Point (Zfh) on v1.0~
* ~Minimal Half-Precision Floating-Point (Zfhmin) on v1.0~
* ~Single-Precision Floating-Point in Integer Register (Zfinx) on v1.0~
* ~Half-Precision Floating-Point in Integer Register (Zhinx) on v1.0~
* ~Minimal Half-Precision Floating-Point in Integer Register (Zhinxmin) on v1.0~

r? `@Amanieu`

Author: bors