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

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/include/configs/p3p440.h b/include/configs/p3p440.h
index 255e072..139175e 100644
--- a/include/configs/p3p440.h
+++ b/include/configs/p3p440.h
@@ -118,7 +118,7 @@
  * Default configuration (environment varibles...)
  *----------------------------------------------------------------------*/
 #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