This patch introduces a implementation of NVMe subsystems,
controllers and discovery service which allows to export
NVMe namespaces across fabrics such as Ethernet, FC etc.

The implementation conforms to the NVMe 1.2.1 specification
and interoperates with NVMe over fabrics host implementations.

Configuration works using configfs, and is best performed using
the nvmetcli tool from http://git.infradead.org/users/hch/nvmetcli.git,
which also has a detailed explanation of the required steps in the
README file.

Signed-off-by: Armen Baloyan
Signed-off-by: Anthony Knapp
Signed-off-by: Jay Freyensee
Signed-off-by: Ming Lin
Signed-off-by: Sagi Grimberg
Signed-off-by: Christoph Hellwig
Reviewed-by: Steve Wise
Signed-off-by: Jens Axboe