drm/i915/guc: drop guc shared area

Recent GuC doesn't require the shared area. We still have one user in
i915 (engine reset via guc) because we haven't updated the command to
match the current guc submission flow [1]. Since the flow in guc is
about to change again, just disable the command for now and add a note
that we'll implement it as part of the new flow.

[1] https://patchwork.freedesktop.org/patch/295038/



Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Fernando Pacheco <fernando.pacheco@intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20191031013040.25803-2-daniele.ceraolospurio@intel.com