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/lib/display_options.c b/lib/display_options.c
index d0480f5..694d2f2 100644
--- a/lib/display_options.c
+++ b/lib/display_options.c
@@ -23,13 +23,12 @@
 
 #include <config.h>
 #include <common.h>
+#include <version.h>
 #include <linux/ctype.h>
 #include <asm/io.h>
 
 int display_options (void)
 {
-	extern char version_string[];
-
 #if defined(BUILD_TAG)
 	printf ("\n\n%s, Build: %s\n\n", version_string, BUILD_TAG);
 #else