RFR: 8290154: [JVMCI] partially implement JVMCI for RISC-V [v12]

[Sacha Coppey]

> This patch adds a partial JVMCI implementation for RISC-V, to allow using the GraalVM Native Image RISC-V LLVM backend, which does not use JVMCI for code emission.
> It creates the jdk.vm.ci.riscv64 and jdk.vm.ci.hotspot.riscv64 packages, as well as implements a part of jvmciCodeInstaller_riscv64.cpp. To check for correctness, it enables JVMCI code installation tests on RISC-V. More testing is performed in Native Image.

Sacha Coppey has updated the pull request incrementally with one additional commit since the last revision:

  Replace RegisterImpl and FloatRegisterImpl uses by Register and FloatRegister

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9587/files
  - new: https://git.openjdk.org/jdk/pull/9587/files/46159813..225fee42

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9587&range=11
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9587&range=10-11

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/9587.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9587/head:pull/9587

PR: https://git.openjdk.org/jdk/pull/9587