drm/i915/gt: Always flush the submission queue on checking for idle

We check for idle during debug prints and other debugging actions.
Simplify the flow by not touching execlists state.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210205174358.28465-1-chris@chris-wilson.co.uk


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>