[riscv-port-jdk17u:riscv-port] RFR: 8306667: RISC-V: Fix storeImmN0 matching rule by using zr register

[Xiaolin Zheng]

Backporting `8306667: RISC-V: Fix storeImmN0 matching rule by using zr register` to fix the crash. Applies cleanly.

Verified using `-Xcomp -XX:HeapBaseMinAddress=72030M`.

Testing a hotspot tier1~2 in progress.

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Commit messages:
 - 8306667: RISC-V: Fix storeImmN0 matching rule by using zr register

Changes: https://git.openjdk.org/riscv-port-jdk17u/pull/51/files
 Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=51&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306667
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/riscv-port-jdk17u/pull/51.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk17u.git pull/51/head:pull/51

PR: https://git.openjdk.org/riscv-port-jdk17u/pull/51