nvme-cli: id-ctrl: Add vendor fields in JSON id-ctrl.

nvme-cli: id-ctrl: Add vendor fields in JSON id-ctrl.

As a part of the id-ctrl command vendor specific callback is issued.
This patch allows the vendor-specific callback to print the extended
vendor unique (ctrl->vs) information from identify controller
data structure in the JSON format. It also enables id-ctrl command
to print vendor specific fields along with generic id-ctrl fields
in one JSON object. This modifies Intel plug-in which is the only
one uses extended id-ctrl (cs->vs) information in current
implementation.

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@hgst.com>