Claude review: drm/vmwgfx: Check vrefresh in drm_mode_setcrtc.

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

Patch Review

**Good refactoring of GPU_TILE_SIZE.** Moving the `GPU_TILE_SIZE` define and associated logic from `vmwgfx_stdu.c` to the shared `vmwgfx_kms.h`/`vmwgfx_kms.c` is the right approach since the mode validation now applies to all display unit types, not just STDU.

**The `mode_valid` callback is the correct hook.** Adding `vmw_kms_config_mode_valid` to `drm_mode_config_funcs` makes this validation apply during `drm_mode_setcrtc`, which is exactly what the failing IGT test exercises.

**Potential duplicate validation for STDU.** With this patch, STDU connectors will validate vrefresh twice — once in `vmw_stdu_connector_mode_valid` and once in the new `vmw_kms_config_mode_valid`. The duplication is harmless but worth noting. Also, the config-level `mode_valid` checks `dev_priv->max_primary_mem` while the STDU connector checks `dev_priv->max_mob_size` — these are intentionally different limits applied at different levels, which is correct.

**The vrefresh check is correct:**
```c
	if (!drm_mode_vrefresh(mode))
		return MODE_BAD;
```
This rejects modes where the calculated vrefresh is zero, which handles the overflow case the IGT test checks.

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