orinoco: Prepare cleanup of powerpc's asm/prom.h

powerpc's asm/prom.h brings some headers that it doesn't
need itself.

In order to clean it up, first add missing headers in
users of asm/prom.h

Signed-off-by: Christophe Leroy <[e-mail]>
Signed-off-by: Kalle Valo <[e-mail]>
Link: https://lore.kernel.org/r/4e3bfd4f[e-mail]

drivers/net/wireless/intersil/orinoco/airport.c

···
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/delay.h>
+#include <linux/of_device.h>
 #include <asm/pmac_feature.h>
 
 #include "orinoco.h"