RFR: 8356159: RISC-V: Add Zabha [v4]

[Robbin Ehn]

> Hi, please consider.
> 
> This adds the byte and halfword atomic memory operations (Zabha) - https://github.com/riscv/riscv-zabha.
> All amo-instructions, except load-reserve and store-conditional, can also be performed on natural aligned half-words and bytes. (i.e. the extension do not add lr.h/b or sc.h/b) This includes amocas if zacas extension is present.
> 
> The majority of this patch is to support amocas.h/b. We are now starting to really feel the pain of all these extensions, as CAS:ing 16/8-bits can now be done in three different ways:
> - lr.w/sc.w 'narrow' CAS (no extension)
> - amocas.w 'narrow' CAS (Zacas)
> - amocas.h/b (Zacas + Zabha)
> 
> There is no hwprobe support yet.
> 
> Ran t1-3 with Zacas+Zabha and t1 without Zabha in qemu.
> 
> Thanks, Robbin

Robbin Ehn has updated the pull request incrementally with one additional commit since the last revision:

  Review fix

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/25252/files
  - new: https://git.openjdk.org/jdk/pull/25252/files/1d43cdb9..73bed21a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25252&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25252&range=02-03

  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/25252.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25252/head:pull/25252

PR: https://git.openjdk.org/jdk/pull/25252