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/md/raid10.c b/drivers/md/raid10.c
index 245640b..26ae74f 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1062,7 +1062,6 @@
 	const int rw = bio_data_dir(bio);
 	const unsigned long do_sync = (bio->bi_rw & REQ_SYNC);
 	const unsigned long do_fua = (bio->bi_rw & REQ_FUA);
-	const unsigned long do_sec = (bio->bi_rw & REQ_SECURE);
 	unsigned long flags;
 	struct md_rdev *blocked_rdev;
 	struct blk_plug_cb *cb;
@@ -1362,7 +1361,7 @@
 							      rdev));
 			mbio->bi_bdev = rdev->bdev;
 			mbio->bi_end_io	= raid10_end_write_request;
-			bio_set_op_attrs(mbio, op, do_sync | do_fua | do_sec);
+			bio_set_op_attrs(mbio, op, do_sync | do_fua);
 			mbio->bi_private = r10_bio;
 
 			atomic_inc(&r10_bio->remaining);
@@ -1404,7 +1403,7 @@
 						   r10_bio, rdev));
 			mbio->bi_bdev = rdev->bdev;
 			mbio->bi_end_io	= raid10_end_write_request;
-			bio_set_op_attrs(mbio, op, do_sync | do_fua | do_sec);
+			bio_set_op_attrs(mbio, op, do_sync | do_fua);
 			mbio->bi_private = r10_bio;
 
 			atomic_inc(&r10_bio->remaining);