drivers: clean-up prom.h implicit includes

Powerpc is a mess of implicit includes by prom.h. Add the necessary
explicit includes to drivers in preparation of prom.h cleanup.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Grant Likely <grant.likely@linaro.org>
diff --git a/drivers/watchdog/mpc8xxx_wdt.c b/drivers/watchdog/mpc8xxx_wdt.c
index da27520..d0ebeba 100644
--- a/drivers/watchdog/mpc8xxx_wdt.c
+++ b/drivers/watchdog/mpc8xxx_wdt.c
@@ -24,6 +24,7 @@
 #include <linux/kernel.h>
 #include <linux/timer.h>
 #include <linux/miscdevice.h>
+#include <linux/of_address.h>
 #include <linux/of_platform.h>
 #include <linux/module.h>
 #include <linux/watchdog.h>