PR #11649: [GPU] Rename and better describe flags related to GEMM fusions.
PR #11649: [GPU] Rename and better describe flags related to GEMM fusions.

Imported from GitHub PR https://github.com/openxla/xla/pull/11649

Rename one flag for consistency because fusions can use different backends.

Also clarify descriptions of other 2 related flags.
Copybara import of the project:

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e82637723b3252b9218ded171b026ff4f860e835 by Ilia Sergachev <isergachev@nvidia.com>:

[GPU] Rename and better describe flags related to GEMM fusions.

Rename one flag for consistency because fusions can use different backends.

Also clarify descriptions of other 2 related flags.

Merging this change closes #11649

FUTURE_COPYBARA_INTEGRATE_REVIEW=https://github.com/openxla/xla/pull/11649 from openxla:rename_dump_flag e82637723b3252b9218ded171b026ff4f860e835
