bootutil: Add TLV for correct ED25519 usage

The pure ED25519 TLV has stores ED25519 signature over SHA512 of
image, rather than signature over SHA512 of SHA256 of image.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>

boot/bootutil/include/bootutil/image.h

@@ -94,6 +94,7 @@ struct flash_area;
 #define IMAGE_TLV_ECDSA_SIG 0x22 /* ECDSA of hash output */
 #define IMAGE_TLV_RSA3072_PSS 0x23 /* RSA3072 of hash output */
 #define IMAGE_TLV_ED25519 0x24 /* ed25519 of hash output */
+#define IMAGE_TLV_ED25519_PURE 0x25 /* ed25519 over SHA512 of the image */
 #define IMAGE_TLV_ENC_RSA2048 0x30 /* Key encrypted with RSA-OAEP-2048 */
 #define IMAGE_TLV_ENC_KW 0x31 /* Key encrypted with AES-KW 128 or 256*/
 #define IMAGE_TLV_ENC_EC256 0x32 /* Key encrypted with ECIES-EC256 */