Fix quoting problem (preboot setting) in many board config files.

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/include/configs/NC650.h b/include/configs/NC650.h
index c051a35..5346545 100644
--- a/include/configs/NC650.h
+++ b/include/configs/NC650.h
@@ -72,7 +72,7 @@
 #define CONFIG_BOOT_RETRY_TIME		900
 #define CONFIG_BOOT_RETRY_MIN		30
 
-#define CONFIG_PREBOOT	"echo;echo Type \"run flash_nfs\" to mount root filesystem over NFS;echo"
+#define CONFIG_PREBOOT	"echo;echo Type \\\"run flash_nfs\\\" to mount root filesystem over NFS;echo"
 
 #undef	CONFIG_BOOTARGS
 #define CONFIG_BOOTCOMMAND							\