RFR: 8357056: RISC-V: Asm fixes - load/store width

[Robbin Ehn]

Hi, please consider.

While working on https://github.com/openjdk/jdk/pull/25252, I notice:
- Major op code was just repeat
- Width coded in binary
- Stores have mixed up rs1 and rs2
- Bonus, fsd used a macro for no reason

I think this improves readability.

Tested tier1

Thanks, Robbin

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

Commit messages:
 - Fixes

Changes: https://git.openjdk.org/jdk/pull/25253/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25253&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357056
  Stats: 148 lines in 1 file changed: 87 ins; 28 del; 33 mod
  Patch: https://git.openjdk.org/jdk/pull/25253.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25253/head:pull/25253

PR: https://git.openjdk.org/jdk/pull/25253