drm/xe/vf: Add debugfs entries to test VF double migration

VF migration sends a marker to the GUC before resource fixups begin,
and repeats the marker with the RESFIX_DONE notification. This prevents
the GUC from submitting jobs during double migration events.

To reliably test double migration, a second migration must be triggered
while fixups from the first migration are still in progress. Since fixups
complete quickly, reproducing this scenario is difficult. Introduce
debugfs controls to add delays in the post-fixup phase, creating a
deterministic window for subsequent migrations.

New debugfs entries:
	/sys/kernel/debug/dri/BDF/
	├── tile0
	│   ├─gt0
	│   │ ├──vf
	│   │ │  ├── resfix_stoppers

resfix_stoppers: Predefined checkpoints that allow the migration process
to pause at specific stages. The stages are given below.

VF_MIGRATION_WAIT_RESFIX_START		- BIT(0)
VF_MIGRATION_WAIT_FIXUPS		- BIT(1)
VF_MIGRATION_WAIT_RESTART_JOBS		- BIT(2)
VF_MIGRATION_WAIT_RESFIX_DONE		- BIT(3)

Each state will pause with a 1-second delay per iteration, continuing until
its corresponding bit is cleared.

Signed-off-by: Satyanarayana K V P <satyanarayana.k.v.p@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Tomasz Lis <tomasz.lis@intel.com>
Acked-by: Adam Miszczak <adam.miszczak@linux.intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://patch.msgid.link/20251201095011.21453-10-satyanarayana.k.v.p@intel.com

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