add PCI device info to ghwc

[jaypipes]

Adds a new ghwc pci subcommand that lists PCI devices. Deprecates the
old PCIInfo.Products, PCIInfo.Classes and PCIInfo.Vendors maps because
these are now fully contained in the github.com/jaypipes/pcidb library.

[jaypipes@thelio ghw]$ go run cmd/ghwc/main.go pci
PCI (45 devices)
[jaypipes@thelio ghw]$ go run cmd/ghwc/main.go pci --format yaml | head -n30
pci:
  Devices:
  - address: "0000:00:00.0"
    class:
      id: "06"
      name: Bridge
    product:
      id: "1450"
      name: Family 17h (Models 00h-0fh) Root Complex
    programming_interface:
      id: "00"
      name: unknown
    subclass:
      id: "00"
      name: Host bridge
    subsystem:
      id: "1450"
      name: unknown
    vendor:
      id: "1022"
      name: Advanced Micro Devices, Inc. [AMD]
  - address: "0000:00:00.2"
    class:
      id: "08"
      name: Generic system peripheral
    product:
      id: "1451"
      name: Family 17h (Models 00h-0fh) I/O Memory Management Unit
    programming_interface:
      id: "00"

Issue #207

[ffromani]

Is not clear to me if calling ListDevices() is now deprecated or still fully supported. Both approaches works from client perspective. As API consumer I for myself prefer to have functions as part of the APIs (e.g. calling ListDevices() explicitely to get a fresh list of devices) but this is mostly personal taste.

[jaypipes]

I replaced ListDevices() with a PCIInfo.Devices slice to make the interface match the other "XXXInfo" structs for consistency purposes. I've gone ahead and deprecated the ListDevices exported function and will unexport it in the v1.0 release (as of yet, I don't have a release date target for v1.0 though) :)

[ffromani]

looks good with a question inside about the API.