drm/xe: Add fault-inject based VRAM page offline injection

Add a fault-inject based debugfs interface for testing VRAM page
offlining. This replaces the previous standalone debugfs approach
with the standard kernel fault-inject infrastructure.

Two debugfs entries are created under the xe debugfs root for
CRI platforms:
- inject_mempage_offline/: Standard fault-inject knobs (probability,
  times, interval, etc.) created by fault_create_debugfs_attr().
  Without CONFIG_FAULT_INJECTION_DEBUG_FS, the stub returns
  ERR_PTR(-ENODEV) and no knobs are created, making the trigger
  effectively a no-op.
- inject_mempage_offline_trigger: Write a PFN value to inject a
  specific page, or write "0" to auto-pick the last unallocated
  VRAM page

The trigger accepts:
- "0"      : auto-pick last unallocated page
- "0xPFN"  : inject fault at a specific PFN address

Usage:
  echo 100 > inject_mempage_offline/probability
  echo 1 > inject_mempage_offline/times
  echo 0 > inject_mempage_offline_trigger

  probability: likelihood of should_fail() returning true (0-100)
  times: number of times injection is allowed (-1 for unlimited)

v7:
- Use PAGE_SIZE
v6(Himal):
- Add warning to rebind driver post test run
v5(Sashiko):
- exclude SRIOV and remove dpa_base addition, already absolute dpa
v4(Himal):
- Use xe_fault_mempage_offline() instead of IS_ENABLED() +
  direct should_fail(). CONFIG_FAULT_INJECTION_DEBUG_FS is now
  an implicit requirement for the trigger to function.
v3(Himal):
- Use FAULT_ACTION
v2(sashiko):
- use cond_resched()
- validate input first and fix addr < 0 case
- validate vr, move block, found var as local to scope_guard

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/20260903161553.528932-32-tejas.upadhyay@intel.com

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