hw/nvme: Add support for Primary Controller Capabilities

Implementation of Primary Controller Capabilities data
structure (Identify command with CNS value of 14h).

Currently, the command returns only ID of a primary controller.
Handling of remaining fields are added in subsequent patches
implementing virtualization enhancements.

Signed-off-by: Lukasz Maniak <lukasz.maniak@linux.intel.com>
Reviewed-by: Klaus Jensen <k.jensen@samsung.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>