PCI: Document pci_ids.h addition policy.

IDs should generally only be added to pci_ids.h when they're shared
across several files in the tree.  IDs that are just used by a single
driver should be defined in the driver instead.

Perhaps documenting this is a good idea to prevent things being moved there,
as it still seems to be happening judging from the git log.

(based on discussion w/gregkh and others).
Acked-by: NGreg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: NDave Jones <davej@redhat.com>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>

include/linux/pci_ids.h

@@ -2,6 +2,9 @@
  *	PCI Class, Vendor and Device IDs
  *
  *	Please keep sorted.
+ *
+ *	Do not add new entries to this file unless the definitions
+ *	are shared between multiple drivers.
  */
 
 /* Device classes and subclasses */