blk-mq-debugfs: Add decode for BLK_MQ_F_TAG_HCTX_SHARED

Showing the hctx flags for when BLK_MQ_F_TAG_HCTX_SHARED is set gives
something like:

root@debian:/home/john# more /sys/kernel/debug/block/sda/hctx0/flags
alloc_policy=FIFO SHOULD_MERGE|TAG_QUEUE_SHARED|3

Add the decoding for that flag.

Fixes: 32bc15af ("blk-mq: Facilitate a shared sbitmap per tagset")
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq-debugfs.c

@@ -246,6 +246,7 @@ static const char *const hctx_flag_name[] = {
 	HCTX_FLAG_NAME(BLOCKING),
 	HCTX_FLAG_NAME(NO_SCHED),
 	HCTX_FLAG_NAME(STACKING),
+	HCTX_FLAG_NAME(TAG_HCTX_SHARED),
 };
 #undef HCTX_FLAG_NAME