RFR: 8320697: RISC-V: Small refactoring for runtime calls [v3]

[Feilong Jiang]

> Hi, please review this refactoring for runtime calls.
> Major changes:
> 1. Unified the runtime calls with the existing MacroAssembler::rt_call. This will remove the duplicate code like `relocate(target.rspec() [&] {...}` to emit uncompressed instructions.
> 2. Removed MacroAssembler::far_branches and made the call sites default to far branches. `branch_range` is 1MB for riscv, and `ReservedCodeCacheSize` will always bigger than `branch_range` in practice. We should remove this unnecessary check and simplify the code logic.
> 3. Renamed MacroAssembler::la_patchable with MacroAssembler::la making it less confusing.
> 4. `far_call` in `rt_call` should use `tmp` instead of the default temporary register `t0`
> 5. Removed some unused codes in `g1BarrierSetAssembler_riscv.cpp`
> 
> 
> Testing:
> - [x] Tier1-3 tested on hifive unmatched board (release)
> - [x] Run non-trivial benchmark workloads (fastdebug)

Feilong Jiang has updated the pull request incrementally with one additional commit since the last revision:

  remove unnecessary relocate

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/16816/files
  - new: https://git.openjdk.org/jdk/pull/16816/files/81347a99..fee7449a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16816&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16816&range=01-02

  Stats: 6 lines in 1 file changed: 0 ins; 4 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/16816.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16816/head:pull/16816

PR: https://git.openjdk.org/jdk/pull/16816