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

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/include/configs/walnut.h b/include/configs/walnut.h
index 19b29e7..b83660c 100644
--- a/include/configs/walnut.h
+++ b/include/configs/walnut.h
@@ -43,7 +43,7 @@
 #define CONFIG_SYS_CLK_FREQ	33333333 /* external frequency to pll	*/
 
 #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