nvme: introduce namespace features flag

Replace the specific ext boolean (that implies on extended LBA format)
with a feature in the new namespace features flag. This is a preparation
for adding more namespace features (such as metadata specific features).

Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Israel Rukshin <israelr@mellanox.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>