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

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/include/configs/BC3450.h b/include/configs/BC3450.h
index 5c2bfc9..3d09ee7 100644
--- a/include/configs/BC3450.h
+++ b/include/configs/BC3450.h
@@ -215,7 +215,7 @@
 #define CONFIG_ZERO_BOOTDELAY_CHECK	/* check for keypress on bootdelay==0 */
 
 #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