Claude review: drm/amdgpu: add VRAM migration infrastructure for drm_pagemap

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

Patch Review

**SPDX comment style:** The `.c` file uses `/* SPDX-License-Identifier: GPL-2.0 OR MIT */` which is the comment style for header files. C source files should use `// SPDX-License-Identifier: GPL-2.0 OR MIT`.

**`drm_pagemap_init` error path leaks resources:**
```c
if (drm_pagemap_init(&svm_dm->dpagemap, pgmap, adev_to_drm(adev),
						&amdgpu_svm_drm_pagemap_ops)) {
	dev_err(adev->dev, "SVM: failed to init drm_pagemap\n");
	return -EINVAL;
}
```
If `drm_pagemap_init()` fails, the `devm_memremap_pages()` registration is not unwound. While devres will eventually clean it up at device teardown, the function has already registered ZONE_DEVICE pages that will have no functional `drm_pagemap` backing — this is a window for use-after-free if the SVM paths try to use them. The error path should call `devm_memunmap_pages()` or equivalent, similar to the `IS_ERR(r)` path above it.

**Alignment in `drm_pagemap_init` call:**
```c
if (drm_pagemap_init(&svm_dm->dpagemap, pgmap, adev_to_drm(adev),
						&amdgpu_svm_drm_pagemap_ops)) {
```
The continuation line has excessive indentation (tabs to column ~40). Align to the opening parenthesis or use a single extra tab.

**`amdgpu_amdkfd.h` include removed but no explanation:** The diff removes `#include "amdgpu_amdkfd.h"` from the includes. Patch 2 replaces the include list entirely, so this is fine functionally, but it's an artifact of the patch split — patch 1 adds the file, patch 2 rewrites the includes. The original file in patch 1 never needed this include in the first place (nothing from amdkfd is used), so this is just slightly messy.

**`amdgpu_svm_page_to_apagemap` is defined but unused in this patch.** It's used later in patch 2. This is minor but could trigger a compiler warning depending on config.

**Double blank line** at line 291 (between `amdgpu_svm_page_to_apagemap` and `amdgpu_svm_drm_pagemap_ops`).

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