nvme-pci: Add support for variable IO SQ element size

The size of a submission queue element should always be 6 (64 bytes)
by spec.

However some controllers such as Apple's are not properly implementing
the standard and require a different size.

This provides the ground work for the subsequent quirks for these
controllers.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Minwoo Im <minwoo.im.dev@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
diff --git a/include/linux/nvme.h b/include/linux/nvme.h
index 32c25b4..f61d690 100644
--- a/include/linux/nvme.h
+++ b/include/linux/nvme.h
@@ -140,6 +140,7 @@ enum {
  * Submission and Completion Queue Entry Sizes for the NVM command set.
  * (In bytes and specified as a power of two (2^n)).
  */
+#define NVME_ADM_SQES       6
 #define NVME_NVM_IOSQES		6
 #define NVME_NVM_IOCQES		4