drm/i915/guc: Do not partition WOPCM if GuC is not used

There seems to be no reason for doing extra work on WOPCM partitioning
in the case GuC is not used, as the partitioning will not be used by the
intel_wopcm_init_hw function anyway.

Signed-off-by: Jakub Bartmiński <jakub.bartminski@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180727141148.30874-2-jakub.bartminski@intel.com