nvmf_proto.h: Update for use in FreeBSD

• Replace SPDK_STATIC_ASSERT with _Static_assert.

• Remove SPDK_ and spdk_ prefixes from types and constants.

• Switch to using FreeBSD headers, e.g. <dev/nvme/nvme.h> in place of "spdk/nvme_spec.h".

• Add a definition of NVME_NQN_FIELD_SIZE (from SPDK's nvme_spec.h).

• Remove constant for the fabrics opcode as this is already present in <dev/nvme/nvme.h>.

• Use types from <dev/nvme/nvme.h> for NVMe structures including struct nvme_sgl_descriptor, struct nvme_command, and struct nvme_completion.

• Use plain uint16_t in place of struct spdk_nvme_status.

Reviewed by: imp
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D44704