AMDGPU: add hotswap entry trampoline lit coverage

[harsh-amd]

Summary:

• Expanded LIT coverage for the hotswap entry-trampoline support merged in AMDGPU: add hotswap entry trampoline core #3008.
• Adds B0/A0 stepping interaction coverage for opt-in entry trampolines.
• Adds gfx125x target coverage for gfx1251 and generic gfx12.5 inputs.
• Adds multi-kernel descriptor rewrite coverage.
• Adds barrier/isfirst interaction coverage.
• Updates hotswap-rewrite-e2e.hip comments and target-note checks to match the current gfx1250 smoke-test behavior.

This PR is intentionally LIT-only. The implementation-redundancy feedback from #3008 is better handled in a follow-up refactor instead of mixing cleanup into this coverage PR.

Verification:

• Rebased onto amd-staging after AMDGPU: add hotswap entry trampoline core #3008 merged.
• build/bin/llvm-lit -sv build/tools/comgr/test-lit --filter hotswap passed: 53 tests.