RFR: 8297851: Add devkit for RISC-V

[Magnus Ihse Bursie]

We should add devkit support for linux/riscv64.

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Commit messages:
 - 8297851: Add devkit for RISC-V

Changes: https://git.openjdk.org/jdk/pull/11432/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11432&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297851
  Stats: 83 lines in 3 files changed: 60 ins; 7 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/11432.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11432/head:pull/11432

PR: https://git.openjdk.org/jdk/pull/11432