[riscv-port-jdk11u:riscv-port] RFR: 8294366: RISC-V: Partially mark out incompressible regions

[Dingli Zhang]

Hi,
Please help review this backport to riscv-port-jdk11u.

Backport of [JDK-8294366](https://bugs.openjdk.org/browse/JDK-8294366).

The original patch cannot be directly applied because of riscv-port-jdk11u do not have `BarrierSetAssembler::nmethod_entry_barrier`, [JDK-8223173](https://bugs.openjdk.org/browse/JDK-8223173) or [JDK-8223173](https://bugs.openjdk.org/browse/JDK-8293007).

Testing:
- Tier1 passed without new failure on lp4a (release).

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Commit messages:
 - 8294366: RISC-V: Partially mark out incompressible regions

Changes: https://git.openjdk.org/riscv-port-jdk11u/pull/43/files
  Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk11u&pr=43&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294366
  Stats: 107 lines in 6 files changed: 46 ins; 36 del; 25 mod
  Patch: https://git.openjdk.org/riscv-port-jdk11u/pull/43.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk11u.git pull/43/head:pull/43

PR: https://git.openjdk.org/riscv-port-jdk11u/pull/43