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

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/include/configs/korat.h b/include/configs/korat.h
index 7f2b09a..88e50d7 100644
--- a/include/configs/korat.h
+++ b/include/configs/korat.h
@@ -170,7 +170,7 @@
 #define CFG_DTT_MIN_TEMP	-30
 
 #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