drm/xe: Split GuC communication initialization

drm/xe: Split GuC communication initialization

Soon we will be trying to communicate with the GuC firmware very
early during VF driver probe, before we finish normal init steps.
Split GuC communication initialization code so the GuC MMIO based
communication xe_guc_mmio_send() functions will work where needed.

Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20240111162051.585-1-michal.wajdeczko@intel.com
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>