nvme: generalize the nvme_multi_css check in nvme_scan_ns

Check for multiple command set support early on an error out if is
not supported when a !NVM command set namespace is found.  This
prepares for adding command set independent passthrough support.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Javier González <javier.gonz@samsung.com>
Reviewed-by: Joel Granados <j.granados@samsung.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Kanchan Joshi <joshi.k@samsung.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>