[jdk23u] RFR: 8337780: RISC-V: C2: Change C calling convention for sp to NS

[Fei Yang]

Clean backport of JDK-8337780 to reduce frame size by 16 bytes and improve performance for some C2 runtime stubs as we do not have to save sp on the method entry. Gtest & Tier1-3 tested on linux-riscv64 platform.

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Commit messages:
 - Backport 53db937dd0766695906dc20c1dbbd3228c02fe1e

Changes: https://git.openjdk.org/jdk23u/pull/87/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk23u&pr=87&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337780
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk23u/pull/87.diff
  Fetch: git fetch https://git.openjdk.org/jdk23u.git pull/87/head:pull/87

PR: https://git.openjdk.org/jdk23u/pull/87