RFR: 8338539: New Object to ObjectMonitor mapping: riscv64 implementation

[Gui Cao]

The riscv64 implementation of JDK-8315884 New Object to ObjectMonitor mapping

### Testing:
- [x] tier1-3 & hotspot:tier4 tests (release)
- [x] test/hotspot/jtreg/runtime/Monitor/UseObjectMonitorTableTest.java (release & fastdebug)

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Commit messages:
 - 8338539: New Object to ObjectMonitor mapping: riscv64 implementation

Changes: https://git.openjdk.org/jdk/pull/20621/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20621&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338539
  Stats: 147 lines in 9 files changed: 66 ins; 11 del; 70 mod
  Patch: https://git.openjdk.org/jdk/pull/20621.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20621/head:pull/20621

PR: https://git.openjdk.org/jdk/pull/20621