[riscv-port] RFR: 8278994: riscv: RVC support [v5]

[Xiaolin Zheng]

> Hi team,
> 
> This patch includes the basic definition of the RVC instruction set and some cleanups. Tested a simple `test/hotspot/jtreg/compiler/` folder on qemu.
> 
> Using `<JAVA_HOME>/bin/java -XX:+UnlockExperimentalVMOptions -XX:+UseRVC -XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly -XX:PrintAssemblyOptions=no-aliases,numeric -XX:+PrintStubCode -XX:-TieredCompilation` could show RVC instructions.
> 
> Thanks,
> Xiaolin

Xiaolin Zheng has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  Update licenses to the new year

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Changes:
  - all: https://git.openjdk.java.net/riscv-port/pull/34/files
  - new: https://git.openjdk.java.net/riscv-port/pull/34/files/2accc5b5..84de97e9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=riscv-port&pr=34&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=riscv-port&pr=34&range=03-04

  Stats: 37 lines in 15 files changed: 0 ins; 0 del; 37 mod
  Patch: https://git.openjdk.java.net/riscv-port/pull/34.diff
  Fetch: git fetch https://git.openjdk.java.net/riscv-port pull/34/head:pull/34

PR: https://git.openjdk.java.net/riscv-port/pull/34