Sync mgpu tests with xla_mgpu config

[alekstheod]

Migrate changes from: #592

[Copilot]

Pull request overview

This PR synchronizes multi-GPU test configurations by migrating changes from an upstream XLA pull request. The changes introduce new CI configuration options to better handle multi-GPU and single-GPU test scenarios.

Changes:

• Added logic to handle --config=ci_multi_gpu and --config=ci_single_gpu flags in the test runner
• Created a new ci_multi_gpu configuration that maps to the existing xla_mgpu config

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
build_tools/rocm/run_xla_ci_build.sh	Adds conditional logic to set appropriate tag filters based on CI configuration type (multi-GPU vs single-GPU)
build_tools/rocm/rocm_xla.bazelrc	Maps the new ci_multi_gpu configuration to the existing xla_mgpu test configuration

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