Fix nda(4) PCIe link status output

Differentiate between PCI Express Endpoint devices and Root Complex
Integrated Endpoints in the nda driver. The Link Status and Capability
registers are not valid for Integrated Endpoints and should not be
displayed. The bhyve emulated NVMe device will advertise as being an
Integrated Endpoint.

Reviewed by: imp
Approved byL imp (mentor)
Differential Revision: https://reviews.freebsd.org/D20282