commonlib/cbfs: Add type ids for empty files

We will soon need to handle empty files.

Change-Id: Ia72a4bff7d9bb36f6a6648c3dd89e86593d80761
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/12785
Tested-by: build bot (Jenkins)

src/commonlib/include/commonlib/cbfs_serialized.h

@@ -62,6 +62,8 @@
     Users are welcome to use any other value for their
     components */
 
+#define CBFS_TYPE_DELETED    0x00000000
+#define CBFS_TYPE_DELETED2   0xffffffff
 #define CBFS_TYPE_STAGE      0x10
 #define CBFS_TYPE_PAYLOAD    0x20
 #define CBFS_TYPE_OPTIONROM  0x30