RFR: 8301036: RISC-V: Factor out functions baseOffset & baseOffset32 from MacroAssembler

[Fei Yang]

The functions baseOffset & baseOffset32 from MacroAssembler on RISC-V accept an Address with base_plus_offset mode. They check the range of the offset, add it and base and put the result in a destination register. This duplicates the work of function MacroAssembler::la. We could refactor this part putting the logic of Address legitimization into MacroAssembler::la and use this function instead.

Testing:
  - [x] Bootcycle (release & fastdebug)
  - [x] Tier1-4 (release)
  - [x] Benchmarks: SPECjbb2015 (release)

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Commit messages:
 - 8301036: RISC-V: Factor out functions baseOffset & baseOffset32 from MacroAssembler

Changes: https://git.openjdk.org/jdk/pull/12177/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12177&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301036
  Stats: 65 lines in 3 files changed: 16 ins; 31 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/12177.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12177/head:pull/12177

PR: https://git.openjdk.org/jdk/pull/12177