block: add a separate operation type for secure erase

Instead of overloading the discard support with the REQ_SECURE flag.
Use the opportunity to rename the queue flag as well, and remove the
dead checks for this flag in the RAID 1 and RAID 10 drivers that don't
claim support for secure erase.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c
index c2d5f6f..bf14642 100644
--- a/drivers/mmc/card/queue.c
+++ b/drivers/mmc/card/queue.c
@@ -171,7 +171,7 @@
 	if (card->pref_erase > max_discard)
 		q->limits.discard_granularity = 0;
 	if (mmc_can_secure_erase_trim(card))
-		queue_flag_set_unlocked(QUEUE_FLAG_SECDISCARD, q);
+		queue_flag_set_unlocked(QUEUE_FLAG_SECERASE, q);
 }
 
 /**