block: add a zone condition debug helper

Add a helper to stringify the zone conditions. We use this helper in the
next patch to track zone conditions in tracepoints.

Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/blkdev.h

@@ -952,6 +952,10 @@ static inline unsigned int blk_rq_stats_sectors(const struct request *rq)
 }
 
 #ifdef CONFIG_BLK_DEV_ZONED
+
+/* Helper to convert BLK_ZONE_ZONE_XXX to its string format XXX */
+const char *blk_zone_cond_str(enum blk_zone_cond zone_cond);
+
 static inline unsigned int blk_rq_zone_no(struct request *rq)
 {
 	return blk_queue_zone_no(rq->q, blk_rq_pos(rq));