[Common] Reduce default cfg's SMEM usage for mhc triton kernel

[kainzhong]

Description

Somehow with triton 3.8 it allocates more SMEM for my triton kernels than previous triton 3.6, which causes the mhc tests to fail due to OOM on L40. Add stage=2 to reduce the default config's SMEM usage and let the CI pass for now

Type of change

• Documentation change (change only to the documentation, either a fix or a new content)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Infra/Build change
• Code refactoring

Changes

Please list the changes introduced in this PR:

• Make the mhc proj kernel's default config (the first one) use a smaller stage number to reduce SMEM usage

Checklist:

• I have read and followed the contributing guidelines
• The functionality is complete
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[greptile-apps]

Greptile Summary

This PR reduces shared-memory usage in the mHC Triton projection kernel by adding a two-stage configuration to its pruned configuration set.

• Uses num_stages=2 as the first configuration when Triton autotuning is disabled.
• Makes the lower-shared-memory configuration available during normal autotuning.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
transformer_engine/common/triton/mhc.py	Adds a supported two-stage projection configuration, reducing the disabled-autotuning default’s shared-memory demand without changing kernel reduction semantics.

_{Reviews (2): Last reviewed commit: "Merge branch 'main' into fix_triton_smem..." | Re-trigger Greptile}

[ptrendx]

/te-ci pytorch