[llvm] [AMDGPU][GlobalISel] Enable vector reductions (PR #131413)

[Matt Arsenault via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
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arsenm wrote:

Don't need all the -verify-machineinstrs in these tests.

Also, do we even have test coverage for these for the DAG? Should we just merge the dag/gisel tests into one in the main test directory? 

https://github.com/llvm/llvm-project/pull/131413