[vectorIntrinsics] RFR: 8266775: Add VectorLoadConst node implementation for Arm SVE

[Wang Huang]

* add VectorLoadConst node implementation for Arm SVE by
   * add new data in `generate_iota_indices`
   * `sve_ld1b` these data
  
Thank you for your review. Any suggestion is welcome.

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Commit messages:
 - 8266775: Add VectorLoadConst node implementation for Arm SVE

Changes: https://git.openjdk.java.net/panama-vector/pull/79/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=79&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266775
  Stats: 52 lines in 3 files changed: 48 ins; 4 del; 0 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/79.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/79/head:pull/79

PR: https://git.openjdk.java.net/panama-vector/pull/79