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

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/include/configs/CPU87.h b/include/configs/CPU87.h
index b087eba..3879d9b 100644
--- a/include/configs/CPU87.h
+++ b/include/configs/CPU87.h
@@ -114,7 +114,7 @@
 
 #define CONFIG_PREBOOT								\
 	"echo; "								\
-	"echo Type \"run flash_nfs\" to mount root filesystem over NFS; "	\
+	"echo Type \\\"run flash_nfs\\\" to mount root filesystem over NFS; "	\
 	"echo"
 
 #undef	CONFIG_BOOTARGS