mainboard/rca/rm4100: transition away from device_t

Replace the use of the old device_t definition inside
mainboard/rcs/rm4100.

Change-Id: I8b242eefe796cd93337177fc694ea42c57c53f08
Signed-off-by: Antonello Dettori <dev@dettori.io>
Reviewed-on: https://review.coreboot.org/17300
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

src/mainboard/rca/rm4100/gpio.c

@@ -23,7 +23,7 @@
 /* Early mainboard specific GPIO setup. */
 static void mb_gpio_init(void)
 {
-	device_t dev;
+	pci_devfn_t dev;
 	uint16_t port;
 	uint32_t set_gpio;