drm/xe/pf: Introduce mutex to protect VFs configurations

PF driver will maintain configurations and resources for every VF
and this data could span multiple tiles and/or GTs.  Prepare mutex
to protect data that we will add in upcoming patches.

Reviewed-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240410170338.1199-2-michal.wajdeczko@intel.com