Display physical slot information in lspci -v

Display physical slot information in lspci -v

We've been exposing slot information in /sys/bus/pci/slots for a
long time now (as long as a hotplug driver or slot detection
driver like pci_slot is loaded).

Let's make life better for our users and display that information
in lspci. If slot entries appear in /sys/bus/pci/slots/,
correlate them to PCI devices, and display the information when
lspci -v is issued.

If no slot entries appear in sysfs (due to no modules loaded), do
nothing.

Now you'll see sample output like the following:

23:01.1 Class 0c04: Device 10df:fd00 (rev 01)
	Subsystem: Device 10df:fd00
	Physical Slot: 3
	Flags: bus master, 66MHz, medium devsel, latency 248, IRQ 60
	...

Signed-off-by: Alex Chiang <achiang@hp.com>