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

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/include/configs/v38b.h b/include/configs/v38b.h
index c0b1a15..e24d6f7 100644
--- a/include/configs/v38b.h
+++ b/include/configs/v38b.h
@@ -128,7 +128,7 @@
 #define CONFIG_BOOTDELAY	3	/* autoboot after 3 seconds */
 
 #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