nvme: centralize AEN defines

All the transports were unnecessarilly duplicating the AEN request
accounting. This patch defines everything in one place.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Guan Junxiong <guanjunxiong@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/nvme.h

@@ -90,6 +90,14 @@ enum {
 };
 
 #define NVME_AQ_DEPTH		32
+#define NVME_NR_AEN_COMMANDS	1
+#define NVME_AQ_BLK_MQ_DEPTH	(NVME_AQ_DEPTH - NVME_NR_AEN_COMMANDS)
+
+/*
+ * Subtract one to leave an empty queue entry for 'Full Queue' condition. See
+ * NVM-Express 1.2 specification, section 4.1.2.
+ */
+#define NVME_AQ_MQ_TAG_DEPTH	(NVME_AQ_BLK_MQ_DEPTH - 1)
 
 enum {
 	NVME_REG_CAP	= 0x0000,	/* Controller Capabilities */