Claude review: drm/xe/ras: Add support for error threshold

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

Patch Review

This adds `xe_ras_get_threshold()` and `xe_ras_set_threshold()` using system controller mailbox commands.

**Issues:**

1. **`xe_ras_get_threshold` doesn't check `response.status`**: Same issue as `get_counter` in patch 2. The `xe_ras_get_threshold_response` struct doesn't have an explicit `status` field, so either the firmware doesn't report errors in get responses (which seems unlikely), or the status is embedded in the response somehow but not checked. Meanwhile `xe_ras_set_threshold` properly checks `response.status`. This inconsistency is suspicious — if get-threshold can fail (invalid component, hardware error), how does the firmware signal that?

2. **Inconsistent `guard(xe_pm_runtime)` placement**: In `xe_ras_get_threshold()`, the guard is placed just before the `xe_sysctrl_send_command` call:
```c
	guard(xe_pm_runtime)(xe);
	ret = xe_sysctrl_send_command(&xe->sc, &command, &len);
```
But the subsequent code that reads from `response` (which was populated by the command) runs after the guard scope. Actually, since `guard()` holds until scope exit, this is fine — but it's worth noting that the runtime PM is held across the entire rest of the function including the debug print.

3. **`xe_ras_get_threshold_response` field layout concern**:
```c
struct xe_ras_get_threshold_response {
	struct xe_ras_error_class counter;
	u32 threshold;
	u32 reserved[4];
} __packed;
```
vs `xe_ras_set_threshold_response`:
```c
struct xe_ras_set_threshold_response {
	struct xe_ras_error_class counter;
	u32 reserved;
	u32 threshold;
	u32 status;
	u32 reserved1[2];
} __packed;
```
In the get response, `threshold` is right after `counter`. In the set response, there's a `reserved` field between `counter` and `threshold`. These are different mailbox commands so different layouts are expected, but the inconsistency should be verified against the firmware interface spec.

---
Generated by Claude Code Patch Reviewer