iwlagn: rename iwl-pci.h to iwl-cfg.h

There's nothing PCI(E) specific in this file.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>