drm/i915: Don't show engine information in fdinfo with GuC submission

At present i915 does not fetch busyness information from GuC, resulting in
incorrect busyness values in fdinfo. Because engine information is coupled
with busyness in fdinfo, skip showing client engine information in fdinfo
with GuC submission till fetching busyness is supported in the i915 GuC
submission backend.

v2 (Daniele):
  Make commit title and description more precise
  Add FIXME with brief description at code change
  s/intel_guc_submission_is_used/intel_uc_uses_guc_submission/

v3 (Daniele):
  Drop FIXME in comment

Bug: https://gitlab.freedesktop.org/drm/intel/-/issues/5564


Fixes: 055634e4 ("drm/i915: Expose client engine utilisation via fdinfo")
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/b614c2c61a954de06fbe2c3a7c70d3a91804407e.1649982207.git.ashutosh.dixit@intel.com