[riscv-port-jdk17u:riscv-port] RFR: 8293566: RISC-V: Clean up push and pop registers

[Dingli Zhang]

Please review this backport to riscv-port-jdk17u.
Backport of [JDK-8293566](https://bugs.openjdk.org/browse/JDK-8293566).
The original patch cannot be directly applied because 17u already had [JDK-8295396](https://bugs.openjdk.org/browse/JDK-8295396) (which cleanup useless CompressibleRegions) and [JDK-8295968](https://bugs.openjdk.org/browse/JDK-8295968) (which replace vl1r_v with vl1re8_v).

Testing:
- Tier1-3 passed without new failure on unmacthed (release).

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Commit messages:
 - RISC-V: Clean up push and pop registers

Changes: https://git.openjdk.org/riscv-port-jdk17u/pull/45/files
 Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=45&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293566
  Stats: 63 lines in 5 files changed: 13 ins; 18 del; 32 mod
  Patch: https://git.openjdk.org/riscv-port-jdk17u/pull/45.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk17u.git pull/45/head:pull/45

PR: https://git.openjdk.org/riscv-port-jdk17u/pull/45