dm: eliminate 'split_discard_bios' flag from DM target interface

There is no need to have DM core split discards on behalf of a DM target
now that blk_queue_split() handles splitting discards based on the
queue_limits.  A DM target just needs to set max_discard_sectors,
discard_granularity, etc, in queue_limits.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index adcfe8a..9fdef68 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -2986,11 +2986,6 @@ static void configure_discard_support(struct raid_set *rs)
 		}
 	}
 
-	/*
-	 * RAID1 and RAID10 personalities require bio splitting,
-	 * RAID0/4/5/6 don't and process large discard bios properly.
-	 */
-	ti->split_discard_bios = !!(rs_is_raid1(rs) || rs_is_raid10(rs));
 	ti->num_discard_bios = 1;
 }
 
@@ -3747,6 +3742,15 @@ static void raid_io_hints(struct dm_target *ti, struct queue_limits *limits)
 
 	blk_limits_io_min(limits, chunk_size);
 	blk_limits_io_opt(limits, chunk_size * mddev_data_stripes(rs));
+
+	/*
+	 * RAID1 and RAID10 personalities require bio splitting,
+	 * RAID0/4/5/6 don't and process large discard bios properly.
+	 */
+	if (rs_is_raid1(rs) || rs_is_raid10(rs)) {
+		limits->discard_granularity = chunk_size;
+		limits->max_discard_sectors = chunk_size;
+	}
 }
 
 static void raid_postsuspend(struct dm_target *ti)