Add support for image trust commands

ipxe/local/general.h

@@ -1,5 +1,6 @@
 #define DIGEST_CMD            /* Image crypto digest commands */
 #define DOWNLOAD_PROTO_HTTPS  /* Secure Hypertext Transfer Protocol */      
 #define IMAGE_COMBOOT         /* COMBOOT */
+#define IMAGE_TRUST_CMD	      /* Image trust management commands */
 #define NET_PROTO_IPV6        /* IPv6 protocol */
 #define VLAN_CMD              /* VLAN commands */