drm/amdgpu: Add lockdep annotations for lock ordering validation

Add lockdep annotations to teach lockdep the correct lock hierarchy
and catch ordering violations during development. This follows the
pattern established by dma-resv in drivers/dma-buf/dma-resv.c.

Lock ordering hierarchy (outermost to innermost):

1. userq_sch_mutex   - Global userq scheduler (enforce_isolation)
2. userq_mutex       - Per-context userq (held across queue create/destroy)
3. notifier_lock     - MMU notifier synchronization
4. vram_lock         - VRAM memory allocator
5. reset_domain->sem - GPU reset synchronization
6. reset_lock        - Reset control mutex
7. srbm_mutex        - SRBM register access
8. grbm_idx_mutex    - GRBM index register access
9. mmio_idx_lock     - MMIO index access (spinlock)

The implementation provides:
- Lock ordering training at module init (amdgpu_lockdep_init)
- Lock class association for real driver locks (amdgpu_lockdep_set_class)

Dummy locks are associated with the same class keys as real driver locks
via lockdep_set_class(), ensuring lockdep connects the training ordering
with actual runtime locks.

Testing:
  Build the kernel with CONFIG_PROVE_LOCKING=y (enables CONFIG_LOCKDEP):
    scripts/config --enable PROVE_LOCKING
    scripts/config --enable DEBUG_LOCKDEP
    make -j$(nproc)

  On boot, dmesg should show:
    AMDGPU: Lockdep annotations initialized (9 lock levels)

  The companion IGT test (tests/amdgpu/amd_lockdep) exercises lock-heavy
  GPU code paths concurrently to trigger lockdep warnings on violations:
    sudo ./build/tests/amdgpu/amd_lockdep
    sudo dmesg | grep -A 50 "circular locking dependency"

  IGT subtests:
    concurrent-reset-and-submit  - reset_sem vs submission locks
    concurrent-mmap-and-evict    - mmap_lock vs vram_lock
    concurrent-userptr-and-reset - notifier_lock vs reset_sem
    stress-all-paths             - all of the above simultaneously

  A clean dmesg (no "circular locking dependency" or "possible recursive
  locking detected" messages) confirms no lock ordering violations.

  For CI integration, the test should be run on kernels compiled with
  CONFIG_LOCKDEP=y; dmesg is scanned post-run for lockdep splats.

v2: (Christian)
- Move notifier_lock and vram_lock before reset locks in hierarchy.
  HMM invalidation holds notifier_lock and can wait for GPU reset
  completion, so notifier_lock must be outer to reset_domain->sem.
- Associate dummy locks with lock class keys via lockdep_set_class()
  so lockdep connects training with real driver locks.
- Update commit message to list all 9 lock levels.

Requires CONFIG_PROVE_LOCKING=y to activate.

Cc: Christian Konig <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Reviewed-by: Christian Konig <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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