[riscv-port] RFR: 8278337: riscv: remove unnecessary ld/sd zr around calls [v2]

[kuaiwei]

> It seems zr(x0) is used as stack alignment when saving/restoring registers around calls. But it's unnecessary to ld/st x0 from/to stack. We just need reserve a stack slot in case alignment is required.

kuaiwei has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

8278337: riscv: remove unnecessary ld/sd zr around call

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Changes:
- all: https://git.openjdk.java.net/riscv-port/pull/25/files
- new: https://git.openjdk.java.net/riscv-port/pull/25/files/5f8767ca..ddc32f4e

Webrevs:
- full: https://webrevs.openjdk.java.net/?repo=riscv-port&pr=25&range=01
- incr: https://webrevs.openjdk.java.net/?repo=riscv-port&pr=25&range=00-01

Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
Patch: https://git.openjdk.java.net/riscv-port/pull/25.diff
Fetch: git fetch https://git.openjdk.java.net/riscv-port pull/25/head:pull/25

PR: https://git.openjdk.java.net/riscv-port/pull/25