exynos: Move common smdk5420 things to common file

A few things are common but are not in the common file. Fix this and
rename the file to fit with the other exynos*-common files.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>
diff --git a/include/configs/smdk5420.h b/include/configs/smdk5420.h
index abda141..894ed11 100644
--- a/include/configs/smdk5420.h
+++ b/include/configs/smdk5420.h
@@ -9,9 +9,7 @@
 #ifndef __CONFIG_SMDK5420_H
 #define __CONFIG_SMDK5420_H
 
-#include <configs/exynos5-common.h>
-
-#include <configs/exynos5420.h>
+#include <configs/exynos5420-common.h>
 
 #define CONFIG_SMDK5420			/* which is in a SMDK5420 */