drm/i915/guc: Disable semaphores when using GuC scheduling

Semaphores are an optimization and not required for basic GuC submission
to work properly. Disable until we have time to do the implementation to
enable semaphores and tune them for performance. Also long direction is
just to delete semaphores from the i915 so another reason to not enable
these for GuC submission.

This patch fixes an existing bugs where I915_ENGINE_HAS_SEMAPHORES was
not honored correctly.

v2: Reword commit message
v3:
 (John H)
  - Add text to commit indicating this also fixing an existing bug
v4:
 (John H)
  - s/bug/bugs

Cc: John Harrison <john.c.harrison@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210721215101.139794-14-matthew.brost@intel.com