RFR: 8296435: RISC-V: Small refactoring for increment/decrement

[Feilong Jiang]

The `increment` and `decrement` use t1 as tmp register, while t1 was the flag register in c2.
We can make tmp registers as the arguments of `increment` and `decrement` so that c2 can reuse them.

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Commit messages:
 - fix
 - fix build
 - add tmp register for increment/decrement

Changes: https://git.openjdk.org/jdk/pull/11005/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11005&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296435
  Stats: 42 lines in 3 files changed: 0 ins; 6 del; 36 mod
  Patch: https://git.openjdk.org/jdk/pull/11005.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11005/head:pull/11005

PR: https://git.openjdk.org/jdk/pull/11005