include/program_loading: Add POSTCAR prog type

Now postcar is a standalone stage give it a
proper type.

Change-Id: Ifa6af9cf20aad27ca87a86817e6ad0a0d1de17c8
Signed-off-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>
Reviewed-on: https://review.coreboot.org/29545
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>

src/include/program_loading.h

@@ -36,6 +36,7 @@ enum prog_type {
 	PROG_PAYLOAD,
 	PROG_BL31,
 	PROG_BL32,
+	PROG_POSTCAR,
 };
 
 /*