drm/xe: nuke GuC on unload

On PVC unloading followed by reloading the module often results in a
completely dead machine (seems to be plaguing CI). Resetting the GuC
like we do at load seems to cure it at least when locally testing this.

v2:
  - Move pc_fini into guc_fini. We want to do the GuC reset just after
    calling pc_fini, otherwise we encounter communication failures. It
    also seems like a good idea to do the reset before we start releasing
    the various other GuC resources. In the case of pc_fini there is an
    explicit stop, but for other stuff like logs, ads, ctb there is not.

References: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/542
References: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/597


Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>