[riscv-port] RFR: 8279827: riscv: RVB: Add shift and add instructions

[Feilong Jiang]

This PR implements shift left and add instructions: `sh1add`/`sh2add`/`sh3add`/`sh1add.uw`/`sh2add.uw`/`sh3add.uw`.

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Commit messages:
 - 8279827: riscv: RVB: Add shift and add instructions

Changes: https://git.openjdk.java.net/riscv-port/pull/43/files
 Webrev: https://webrevs.openjdk.java.net/?repo=riscv-port&pr=43&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279827
  Stats: 508 lines in 14 files changed: 259 ins; 107 del; 142 mod
  Patch: https://git.openjdk.java.net/riscv-port/pull/43.diff
  Fetch: git fetch https://git.openjdk.java.net/riscv-port pull/43/head:pull/43

PR: https://git.openjdk.java.net/riscv-port/pull/43