drm/xe/pf: Skip fair VFs provisioning if already provisioned

Our debugfs allows to view and change VFs' provisioning configs.

If we attempt to experiment with VFs provisioning before enabling
them, this early config will affect fair provisioning calculations,
and will also be overwritten, which is undesirable behavior.

To improve this, check if the VFs configs are empty (unprovisioned)
before starting the fair provisioning procedure.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240701102738.934-2-michal.wajdeczko@intel.com