RFR: 8319184: RISC-V: improve MD5 intrinsic [v3]

[Antonios Printezis]

> Tweaks to the RISC-V MD5 intrinsic.
> 
> * do the loads from the buffer more incrementally instead of all in one go
> * don't mask off the top 32 bits of a register before an addw instruction, as addw will ignore them anyway
> * remove the rmask32 register, as the mask is not needed any more (only at the start / end and it's 
> * cleanup some of the register usage

Antonios Printezis has updated the pull request incrementally with one additional commit since the last revision:

  small fix based on code review feedback

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16453/files
  - new: https://git.openjdk.org/jdk/pull/16453/files/d0baae6a..8e13a782

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16453&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16453&range=01-02

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16453.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16453/head:pull/16453

PR: https://git.openjdk.org/jdk/pull/16453