amdfwtool: Add a macro to set explicitly second gen for old SOCs

It is more reasonable than getting the value from memset.

For the reserved bits, keep them as they were for old SOCs.

Change-Id: I65caa11e835d2ff52bec4b8904057bbced434891
Signed-off-by: Zheng Bao <fishbaozi@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/63319
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

util/amdfwtool/amdfwtool.h

@@ -88,6 +88,7 @@ struct second_gen_efs { /* todo: expand for Server products */
 } __attribute__((packed));
 
 #define EFS_SECOND_GEN 0
+#define EFS_BEFORE_SECOND_GEN 1
 
 typedef struct _embedded_firmware {
 	uint32_t signature; /* 0x55aa55aa */