drm/xe/pf: Add sysfs device symlinks to enabled VFs

drm/xe/pf: Add sysfs device symlinks to enabled VFs

For convenience, for every enabled VF add 'device' symlink from
our SR-IOV admin VF folder to enabled sysfs PCI VF device entry.
Remove all those links when disabling PCI VFs.

For completeness, add static 'device' symlink for the PF itself.

  /sys/bus/pci/drivers/xe/BDF/sriov_admin/
  ├── pf
  │   └── device -> ../../../BDF	# PF BDF
  ├── vf1
  │   └── device -> ../../../BDF'	# VF1 BDF
  ├── vf2
  │   └── device -> ../../../BDF"	# VF2 BDF

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patch.msgid.link/20251030222348.186658-16-michal.wajdeczko@intel.com