drm/xe/pf: Expose VF control operations over debugfs

drm/xe/pf: Expose VF control operations over debugfs

To allow the user to control the activity of individual VFs,
expose basic VF control operations (pause, resume, stop, reset)
over the debugfs as write-only files:

  /sys/kernel/debug/dri/BDF/sriov/
  ├── vf1
  │   ├── pause
  │   ├── reset
  │   ├── resume
  │   ├── stop
  │   :
  ├── vf2
  :   :

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>
Link: https://lore.kernel.org/r/20250930233525.201263-4-michal.wajdeczko@intel.com