Claude review: drm/ttm: Be more aggressive when allocating below protection limit

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

Patch Review

This is the core behavioral change. When an allocation is protected by min/low and resource allocation fails, TTM now attempts eviction of unprotected buffers.

**Logic flow**:
```c
if (!alloc_state->in_evict) {
    may_evict |= dmem_cgroup_below_min(NULL, alloc_state->charge_pool);
    alloc_state->may_try_low = may_evict;
    may_evict |= dmem_cgroup_below_low(NULL, alloc_state->charge_pool);
}
```

This is subtly clever:
- If below **min**: `may_evict=true`, `may_try_low=true` (can try evicting low-protected BOs too)
- If below **low** (but not min): `may_evict=true`, `may_try_low=false` (only evict unprotected BOs)
- If neither: no change to `may_evict`, no aggressive eviction

The `may_try_low` flag gates the "retry with low" logic in `ttm_bo_evict_alloc()`, preventing low-but-not-min protected allocations from evicting low-protected buffers. This correctly models the min > low priority.

**Comment style**: The block comment at line 2133 starts with `/* If we failed...` — kernel style prefers the opening `/*` on its own line for multi-line comments. Minor style nit.

**The `may_try_low` field naming** could be slightly confusing since setting it to `true` means "yes, we may try evicting low-protected BOs" but the semantics in `ttm_bo_evict_alloc` are "skip the low retry if may_try_low is false". This is consistent but requires careful reading.

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