drm/xe/vram: Add VRAM page offline fault handler

Add the core VRAM page offlining logic to handle HW-reported faulty
physical addresses:

- xe_ttm_vram_purge_page(): Purges the BO containing the faulty
  address. Bans the associated VM (if page table BO) and exec queue
  (if LRC BO). Moves xe_exec_queue_kill() outside xe_bo_lock() to
  avoid AB-BA deadlock with vm->lock. Uses READ_ONCE(bo->q) to
  safely access the exec queue pointer.

- xe_ttm_vram_page_already_processed(): Checks if an address is
  already tracked in offlined_pages or queued_pages lists to avoid
  double-processing.

- xe_ttm_vram_reserve_page_at_addr(): Two-phase reservation that
  first queues the page, purges the BO outside the lock, then
  reserves the buddy block. Handles both allocated (BO present)
  and free page cases. Returns -EIO for critical kernel BOs to
  trigger system reset.

- xe_ttm_vram_addr_to_region(): Maps a DPA to its corresponding
  VRAM region. Checks if the address falls within usable space,
  or infrastructure zones (CCS, GSM, DSM) where it returns NULL
  to flag a reset path. If the target address is outside any
  known region returns ERR_PTR(-EOPNOTSUPP)

- xe_ttm_vram_handle_addr_fault(): Entry point called by RAS.
  Returns -EEXIST if already processed, -EIO for GSM/critical BO,
  -EOPNOTSUPP if out of bounds.

v15:
- Add immediate reservation for free pages
- Use lock before accessing tbo
v14(Sashiko/MattB):
- Retry queued pages during xe_ttm_vram_mgr_del()
- Move all changes to find owner of bo to its API
v13(Himal):
- Remove redundant code
v12(Sashiko):
- Handle multi tile and add assert for 4K align
- Remove unaligned action comment for ENXIO
v11(Himal):
- match everywhere with enum vs bool for status member
- Fix comment and remove unused var
- if purge fail let next alloc confirm failure
- pass absolute address, useful for multi tile

Assisted-by: Copilot:claude-opus-4.6
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Signed-off-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260903161553.528932-26-tejas.upadhyay@intel.com

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