drm/i915/guc: distinguish HAS_GUC() from HAS_GUC_UCODE/HAS_GUC_SCHED

For now, anything with a GuC requires uCode loading, and then supports
command submission once loaded. But these are logically distinct from
simply "having a GuC", so we need a separate macro for the latter. Then,
various tests should use this new macro rather than HAS_GUC_UCODE() or
testing enable_guc_submission.

v4:
    Added a couple more uses of the new macro.

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>