nvme: Add PCI transport type

nvme: Add PCI transport type

Define the transport type NVMF_TRTYPE_PCI for PCI endpoint targets.
This transport type is defined using the value 0 which is reserved in
the NVMe base specifications v2.1 (Figure 294). Given that struct
nvmet_port are zeroed out on creation, to avoid having this transsport
type becoming the new default, nvmet_referral_make() and
nvmet_ports_make() are modified to initialize a port discovery address
transport type field (disc_addr.trtype) to NVMF_TRTYPE_MAX.

Any port using this transport type is also skipped and not reported in
the discovery log page (nvmet_execute_disc_get_log_page()).

The helper function nvmet_is_pci_ctrl() is also introduced to check if
a target controller uses the PCI transport.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Rick Wertenbroek <rick.wertenbroek@gmail.com>
Tested-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Keith Busch <kbusch@kernel.org>