RFR: 8301033: RISC-V: Handle special cases for MinI/MaxI nodes for Zbb

[Fei Yang]

The code generation for MinI/MaxI nodes for Zbb extension could be improved when one of the source operands is constant 0. We can make use of the dedicated zero register of the architecture for these special cases. This adds two match rules for those cases.

Testing:
  [x] https://github.com/openjdk/jdk/blob/master/test/hotspot/jtreg/compiler/intrinsics/math/TestMinMaxIntrinsics.java
  [x] Tier1 tested with QEMU (Enabled support for Zbb extension)

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Commit messages:
 - 8301033: RISC-V: Handle special cases for MinI/MaxI nodes for Zbb

Changes: https://git.openjdk.org/jdk/pull/12176/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12176&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301033
  Stats: 38 lines in 1 file changed: 34 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/12176.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12176/head:pull/12176

PR: https://git.openjdk.org/jdk/pull/12176