Claude review: drm/amdkfd: Unify userptr cleanup and update paths

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

Patch Review

**Overview:** Refactors cleanup to handle both single and batch allocations.

**Issues:**

1. **Missing Lock - Critical:**
```c
+	if (mem->num_user_ranges > 0 && mem->user_ranges) {
+		for (i = 0; i < mem->num_user_ranges; i++)
+			interval_tree_remove(&mem->user_ranges[i].it_node,
+					     &mem->user_ranges_itree);
```
Modifying the interval tree without holding any lock. This can race with concurrent MMU notifier callbacks.

2. **Use After Free - Critical:**
```c
+		if (mem->batch_notifier.mm) {
+			mmu_interval_notifier_remove(&mem->batch_notifier);
+			mem->batch_notifier.mm = NULL;
+		}
+		kvfree(mem->user_ranges);
```
After removing the notifier, a concurrent invalidation callback could still be running and accessing `mem->user_ranges`. Should ensure all callbacks are complete before freeing.

3. **Race Condition:**
```c
+		mem->user_ranges[i].valid = true;
```
Setting `valid` flag outside of `notifier_lock` can race with invalidation callbacks that clear it.

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Generated by Claude Code Patch Reviewer