ppc4xx: Move gpio.h to ppc4xx-gpio.h since its ppc4xx specific

Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/post/board/lwmon5/watchdog.c b/post/board/lwmon5/watchdog.c
index 44f0488..f181506 100644
--- a/post/board/lwmon5/watchdog.c
+++ b/post/board/lwmon5/watchdog.c
@@ -34,7 +34,7 @@
 #if CONFIG_POST & CONFIG_SYS_POST_WATCHDOG
 
 #include <watchdog.h>
-#include <asm/gpio.h>
+#include <asm/ppc4xx-gpio.h>
 #include <asm/io.h>
 
 static uint watchdog_magic_read(void)