RFR: 8295382: Implement SHA-256 Intrinsic on RISC-V

[Ludovic Henry]

This has been tested with patches currently being submitted to QEMU to add support for Zvkb and Zvknha extensions.

The documentation for the Vector Crypto extension's instructions is available at https://github.com/riscv/riscv-crypto/tree/master/doc/vector/insns

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Commit messages:
 - 8295382: Implement SHA-256 Intrinsic on RISC-V

Changes: https://git.openjdk.org/jdk/pull/12208/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12208&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295382
  Stats: 536 lines in 5 files changed: 530 ins; 1 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/12208.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12208/head:pull/12208

PR: https://git.openjdk.org/jdk/pull/12208