nvme: split out fabrics version of nvme_opcode_str()

nvme_opcode_str() currently supports admin, IO, and fabrics commands.
However, fabrics commands aren't allowed for the pci transport.
Currently the pci caller passes 0 as the fctype,
which means any fabrics command would be displayed as "Property Set".

Move fabrics command support into a function nvme_fabrics_opcode_str()
and remove the fctype argument to nvme_opcode_str().
This way, a fabrics command will display as "Unknown" for pci.
Convert the rdma and tcp transports to use nvme_fabrics_opcode_str().

Signed-off-by: Caleb Sander <csander@purestorage.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Keith Busch <kbusch@kernel.org>