Claude review: drm/vblank: Add DRM_VBLANK_FLAG_SIMULATED

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

Patch Review

Defines the flag and adds the ioctl check.

**Main concern:** `DRM_VBLANK_FLAG_SIMULATED` is defined as `BIT(1)`:
```c
#define DRM_VBLANK_FLAG_SIMULATED	BIT(1)
```
This skips `BIT(0)` with no comment or reserved `BIT(0)` definition. Either start at `BIT(0)` or add a comment explaining what `BIT(0)` is reserved for. As-is, it looks like an accidental off-by-one.

The ioctl check itself is well-placed:
```c
	vblank = drm_vblank_crtc(dev, pipe);

	if (vblank->flags & DRM_VBLANK_FLAG_SIMULATED)
		return -EOPNOTSUPP;
```
This is after the pipe validation but before any vblank counter manipulation, which is correct. The `-EOPNOTSUPP` error code is consistent with the existing `drm_wait_vblank_supported()` check at the top of the same function.

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Generated by Claude Code Patch Reviewer