drm/xe/vf: Skip attempt to start GuC PC if VF

We have already marked the GuC PC feature as not applicable for
VF devices, but we missed the fact that there may be still some
privileged activities performed by this component, who does much
more than its name suggests.

Explicitly skip xe_guc_pc_start() if running as a VF driver and
use a GT oriented message to report any error.

v2: also skip xe_guc_pc_stop (Vinay)

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240622094253.1081-1-michal.wajdeczko@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>