Claude review: drm/amd/display: Export symbols for KUnit test modules

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Correctness: Good.** The three `EXPORT_IF_KUNIT()` additions are placed correctly — immediately after the closing brace of each function definition, consistent with all existing uses in the codebase (e.g., `amdgpu_dm_psr_fill_caps` at `amdgpu_dm_psr.c:92`, `dm_ism_next_state` at `amdgpu_dm_ism.c:131`, etc.).

**Pattern consistency:**
```c
+EXPORT_IF_KUNIT(amdgpu_dm_ism_init);
...
+EXPORT_IF_KUNIT(amdgpu_dm_ism_fini);
...
+EXPORT_IF_KUNIT(amdgpu_dm_psr_set_event);
```
All three follow the same one-liner format used throughout the directory. Both source files already have `#include "amdgpu_dm_kunit_helpers.h"`, so the macro is defined.

**Commit message:** Clear and accurate. The Fixes tags correctly identify the commits that introduced the tests needing these symbols. The `Assisted-by: Copilot:Claude-Opus-4.6` tag is noted.

**Minor nit (non-blocking):** The diff context shows a blank line between `amdgpu_dm_ism_init()` and `amdgpu_dm_ism_fini()` at the export location (lines 142-143 in the diff show two blank lines). The `EXPORT_IF_KUNIT(amdgpu_dm_ism_init)` is placed before those blank lines, while most other uses in the file place the macro right after the closing `}` with one blank line separation before the next function. This is fine — the existing code already had a double blank line there, and the macro placement is correct.

**No issues found.** The patch is minimal, correct, and follows established conventions.

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