Add Zephyr infrastructure for ed25519

Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/boot/zephyr/keys.c b/boot/zephyr/keys.c
index d59afdb..ee61c7d 100644
--- a/boot/zephyr/keys.c
+++ b/boot/zephyr/keys.c
@@ -36,6 +36,10 @@
 #define HAVE_KEYS
 extern const unsigned char ecdsa_pub_key[];
 extern unsigned int ecdsa_pub_key_len;
+#elif defined(MCUBOOT_SIGN_ED25519)
+#define HAVE_KEYS
+extern const unsigned char ed25519_pub_key[];
+extern unsigned int ed25519_pub_key_len;
 #else
 #error "No public key available for given signing algorithm."
 #endif
@@ -54,6 +58,9 @@
 #elif defined(MCUBOOT_SIGN_EC256)
         .key = ecdsa_pub_key,
         .len = &ecdsa_pub_key_len,
+#elif defined(MCUBOOT_SIGN_ED25519)
+        .key = ed25519_pub_key,
+        .len = &ed25519_pub_key_len,
 #endif
     },
 };