RFR: 8295762: [Vector API] Update generate_iota_indices for x86_32 after JDK-8293409

[Jie Fu]

Hi all,

Many vector api tests fail on x86_32 after JDK-8293409 due to computing incorrect results.
The reason is that `generate_iota_indices` was updated only for x86_64 in JDK-8293409.
So let's fix it for x86_32.

Testing:
  - vector api tests on x86_32, all passed

Thanks.
Best regards,
Jie

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Commit messages:
 - 8295762: [Vector API] Update generate_iota_indices for x86_32 after JDK-8293409

Changes: https://git.openjdk.org/jdk/pull/10807/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10807&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295762
  Stats: 91 lines in 1 file changed: 91 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10807.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10807/head:pull/10807

PR: https://git.openjdk.org/jdk/pull/10807