northbridge/intel/nehalem: transition away from device_t

Replace the use of the old device_t definition inside
northbridge/intel/nehalem.

The patch has been tested both with the arch/io.h definition of device_t
enabled and disabled in order to ensure compatibility while the
transaction takes place.

Change-Id: I6da4e0a9ef21b3285f4a369c8ddfbdb32a7a3801
Signed-off-by: Antonello Dettori <dev@dettori.io>
Reviewed-on: https://review.coreboot.org/16406
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

src/northbridge/intel/nehalem/acpi.c

@@ -130,7 +130,7 @@ static int init_opregion_vbt(igd_opregion_t * opregion)
 /* Initialize IGD OpRegion, called from ACPI code */
 int init_igd_opregion(igd_opregion_t * opregion)
 {
-	device_t igd;
+	pci_devfn_t igd;
 	u16 reg16;
 
 	memset((void *)opregion, 0, sizeof(igd_opregion_t));