drm/xe/guc: Unblock GuC buffer cache for all modes

Today we were using GuC buffer cache only in the PF mode, but
shortly we will want to use it also in native and VF mode.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://lore.kernel.org/r/20250512220018.172-2-michal.wajdeczko@intel.com