Update U-Boot's build timestamp on every compile

Use the GNU 'date' command to auto-generate a new U-Boot
timestamp on every compile.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
diff --git a/lib_microblaze/board.c b/lib_microblaze/board.c
index cd61918..250972c 100644
--- a/lib_microblaze/board.c
+++ b/lib_microblaze/board.c
@@ -27,12 +27,13 @@
 #include <common.h>
 #include <command.h>
 #include <malloc.h>
+#include <timestamp.h>
 #include <version.h>
 #include <watchdog.h>
 
 DECLARE_GLOBAL_DATA_PTR;
 
-const char version_string[] = U_BOOT_VERSION " (" __DATE__ " - " __TIME__ ")";
+const char version_string[] = U_BOOT_VERSION " ("U_BOOT_DATE" - "U_BOOT_TIME")";
 
 #ifdef CONFIG_SYS_GPIO_0
 extern int gpio_init (void);