drm/i915/execlists: HWACK checking superseded checking port[0].count

The HWACK bit more generically solves the problem of resubmitting ESLP
while the hardware is still processing the current ELSP write. We no
longer need to check port[0].count itself.

References: ba74cb10 ("drm/i915/execlists: Delay writing to ELSP until HW has processed the previous write")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michel Thierry <michel.thierry@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180517115647.17205-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_lrc.c

@@ -612,8 +612,6 @@ static bool __execlists_dequeue(struct intel_engine_cs *engine)
 		GEM_BUG_ON(!execlists_is_active(execlists,
 						EXECLISTS_ACTIVE_USER));
 		GEM_BUG_ON(!port_count(&port[0]));
-		if (port_count(&port[0]) > 1)
-			return false;
 
 		/*
 		 * If we write to ELSP a second time before the HW has had