mmc: update workqueue usages

Workqueue creation API has been updated and flush_scheduled_work() is
deprecated and scheduled to be removed.

* core/core.c: Use alloc_ordered_workqueue() instead of
  create_singlethread_workqueue().  This removes an unnecessary
  rescuer.

* host/omap.c: Create, use and flush mmc_omap_wq instead of the
  system_wq.

* Flush host->mmc_carddetect_work directly on removal instead of using
  flush_scheduled_work().

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Chris Ball <cjb@laptop.org>
Cc: linux-mmc@vger.kernel.org
diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
index 82a1079..9e136bb 100644
--- a/drivers/mmc/host/omap_hsmmc.c
+++ b/drivers/mmc/host/omap_hsmmc.c
@@ -2290,7 +2290,7 @@
 		free_irq(host->irq, host);
 		if (mmc_slot(host).card_detect_irq)
 			free_irq(mmc_slot(host).card_detect_irq, host);
-		flush_scheduled_work();
+		flush_work_sync(&host->mmc_carddetect_work);
 
 		mmc_host_disable(host->mmc);
 		clk_disable(host->iclk);