drm/xe/pf: Allow bulk change all VFs priority using sysfs

drm/xe/pf: Allow bulk change all VFs priority using sysfs

It is expected to be a common practice to configure the same level
of scheduling priority across all VFs and PF (at least as starting
point). Due to current GuC FW limitations it is also the only way
to change VFs priority.

Add write-only sysfs attribute that will apply required priority
level to all VFs and PF at once.

  /sys/bus/pci/drivers/xe/BDF/
  ├── sriov_admin/
      ├── .bulk_profile
      │   └── sched_priority		[WO] low, normal

Writing "low" to this write-only attribute will change PF and
VFs scheduling priority on all tiles/GTs to LOW (function will
be scheduled only if it has work submitted). Similarly, writing
"normal" will change functions priority to NORMAL (functions will
be scheduled irrespective of whether there is a work or not).

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/20251030222348.186658-13-michal.wajdeczko@intel.com