[riscv-port-jdk11u:riscv-port] RFR: 8294086: RISC-V: Cleanup InstructionMark usages in the backend

[Dingli Zhang]

Hi all, 

Please review this backport to riscv-port-jdk11u.

Backport of [JDK-8294086](https://bugs.openjdk.org/browse/JDK-8294086).

The original patch cannot be directly applied because changes of `MacroAssembler::read_polling_page` and  `macroAssembler_riscv.hpp` have been modified.

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

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Commit messages:
 - 8294086: RISC-V: Cleanup InstructionMark usages in the backend

Changes: https://git.openjdk.org/riscv-port-jdk11u/pull/38/files
  Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk11u&pr=38&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294086
  Stats: 11 lines in 2 files changed: 0 ins; 6 del; 5 mod
  Patch: https://git.openjdk.org/riscv-port-jdk11u/pull/38.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk11u.git pull/38/head:pull/38

PR: https://git.openjdk.org/riscv-port-jdk11u/pull/38