unify version_string

This patch removes the architecture specific implementation of
version_string where possible. Some architectures use a special place
and therefore we provide U_BOOT_VERSION_STRING definition and a common
weak symbol version_string.

Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>
CC: Mike Frysinger <vapier@gentoo.org>
CC: Peter Pan <pppeterpppan@gmail.com>
Acked-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/drivers/video/cfb_console.c b/drivers/video/cfb_console.c
index b427c84..77e7285 100644
--- a/drivers/video/cfb_console.c
+++ b/drivers/video/cfb_console.c
@@ -91,6 +91,7 @@
 */
 
 #include <common.h>
+#include <version.h>
 
 #include <malloc.h>
 
@@ -1458,7 +1459,6 @@
 static void *video_logo (void)
 {
 	char info[128];
-	extern char version_string;
 	int space, len, y_off = 0;
 
 #ifdef CONFIG_SPLASH_SCREEN