drm/panfrost: don't use pfdevfreq.busy_count to know if hw is idle

This use devfreq variable that will be lock with spinlock in future
patches. We should either introduce a function to access this one
but as devfreq is optional let's just remove it.
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Signed-off-by: Clément Péron <peron.clem@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200710095409.407087-4-peron.clem@gmail.com

drivers/gpu/drm/panfrost/panfrost_job.c

@@ -581,10 +581,6 @@ int panfrost_job_is_idle(struct panfrost_device *pfdev)
 	struct panfrost_job_slot *js = pfdev->js;
 	int i;
 
-	/* Check whether the hardware is idle */
-	if (atomic_read(&pfdev->devfreq.busy_count))
-		return false;
-
 	for (i = 0; i < NUM_JOB_SLOTS; i++) {
 		/* If there are any jobs in the HW queue, we're not idle */
 		if (atomic_read(&js->queue[i].sched.hw_rq_count))