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

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/include/configs/QS860T.h b/include/configs/QS860T.h
index 62cf2a4..c980901 100644
--- a/include/configs/QS860T.h
+++ b/include/configs/QS860T.h
@@ -72,7 +72,7 @@
 #undef CONFIG_CLOCKS_IN_MHZ		/* clocks passsed to Linux in MHz */
 
 #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