nvme: consolidate setting the tagset flags

All nvme transports should be using the same flags for their tagsets,
with the exception for the blocking flag that should only be set for
transports that can block in ->queue_rq.

Add a NVME_F_BLOCKING flag to nvme_ctrl_ops to control the blocking
behavior and lift setting the flags into nvme_alloc_{admin,io}_tag_set.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>