nvmet: Add vendor_id and subsys_vendor_id subsystem attributes

nvmet: Add vendor_id and subsys_vendor_id subsystem attributes

Define the new vendor_id and subsys_vendor_id configfs attribute for
target subsystems. These attributes are respectively reported as the
vid field and as the ssvid field of the identify controller data of
a target controllers using the subsystem for which these attributes
are set.

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>