RFR: 8332899: RISC-V: add comment and make the code more readable (if possible) in MacroAssembler::movptr [v2]

[Hamlin Li]

> Hi,
> Can you help to review the patch?
> As discussed, https://github.com/openjdk/jdk/pull/19246#discussion_r1613279908, it's worth to make the code more readable.
> For movptr1, add some comments to help understand the tricky part.
> For movptr2, it uses the similar (tricky) way as movptr1, so I align the code implementation with movptr1, and try to make it more straightforward.
> I tried it, hope it's better.
> Thanks.

Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:

  typo

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19431/files
  - new: https://git.openjdk.org/jdk/pull/19431/files/93de6315..263aefba

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19431&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19431&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/19431.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19431/head:pull/19431

PR: https://git.openjdk.org/jdk/pull/19431