RFR: 8293781: RISC-V: Clarify types of calls [v3]

[Yanhong Zhu]

> RISCV64 OpenJDK uses different types of calls in generated calls. It should be clarified what they are. And the PR also cleans up some out-of-date comments.

Yanhong Zhu has updated the pull request incrementally with one additional commit since the last revision:

  fix a typo

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10311/files
  - new: https://git.openjdk.org/jdk/pull/10311/files/5e99b407..9e77d750

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10311&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10311&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10311.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10311/head:pull/10311

PR: https://git.openjdk.org/jdk/pull/10311