pci: recognize "non-essential instrumentation" devices

Some AMD EPYC VCPUs generated boot message of the type:

pci4: <unknown> at device 0.0 (no driver attached)

These are displayed for device class 0x13 devices, e.g.:

none8@pci0:130:0:0: class=0x130000 rev=0x00 hdr=0x00 vendor=0x1022 \

			device=0x148a subvendor=0x1022 subdevice=0x148a
    vendor     = 'Advanced Micro Devices, Inc. [AMD]'
    device     = 'Starship/Matisse PCIe Dummy Function'
    class      = non-essential instrumentation

Since these devices serve no purpose (no driver attaches) I have
enabled the reporting of suich devices only for verbose boots (a
diversion from the patch provided in the PR).

A verbose boot will now display such devices as:

pci4: <non-essential instrumentation> at device 0.0 (no driver attached)

PR: 263469
Reported by: jfc@mit.edu (John F. Carr)
MFC after: 1 week