drm/radeon: use system_wq instead of dev_priv->wq

With cmwq, there's no reason for radeon to use a dedicated workqueue.
Drop dev_priv->wq and use system_wq instead.

Because radeon_driver_irq_uninstall_kms() may be called from
unsleepable context, the work items can't be flushed from there.
Instead, init and flush from radeon_irq_kms_init/fini().

While at it, simplify canceling/flushing of rdev->pm.dynpm_idle_work.
Always initialize and sync cancel instead of being unnecessarily smart
about it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Alex Deucher <alexdeucher@gmail.com>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/r600.c b/drivers/gpu/drm/radeon/r600.c
index f95ca5b..279794c3 100644
--- a/drivers/gpu/drm/radeon/r600.c
+++ b/drivers/gpu/drm/radeon/r600.c
@@ -3442,7 +3442,7 @@
 	if (wptr != rdev->ih.wptr)
 		goto restart_ih;
 	if (queue_hotplug)
-		queue_work(rdev->wq, &rdev->hotplug_work);
+		schedule_work(&rdev->hotplug_work);
 	rdev->ih.rptr = rptr;
 	WREG32(IH_RB_RPTR, rdev->ih.rptr);
 	spin_unlock_irqrestore(&rdev->ih.lock, flags);