RFR: 8311074: RISC-V: Fix -Wconversion warnings in some code header files [v2]

[Gui Cao]

> Hi, refer to the modification of aarch64 in https://github.com/openjdk/jdk/pull/14675 , here is the riscv version, before this PR has the same -Wconversion warnings as aarch64, after this this PR the -Wconversion warnings has been eliminated.
> Please take a look and have some reviews. Thanks a lot.
> 
> ## Testing:
> - [x] Tier1 tests (release)

Gui Cao has updated the pull request incrementally with one additional commit since the last revision:

  Keep the surrounding spaces for /

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14702/files
  - new: https://git.openjdk.org/jdk/pull/14702/files/d7c47a0d..b2ee8652

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14702&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14702&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14702.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14702/head:pull/14702

PR: https://git.openjdk.org/jdk/pull/14702