Add ed25519 verification to sim

Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/sim/mcuboot-sys/Cargo.toml b/sim/mcuboot-sys/Cargo.toml
index 7512e22..4f20725 100644
--- a/sim/mcuboot-sys/Cargo.toml
+++ b/sim/mcuboot-sys/Cargo.toml
@@ -21,6 +21,9 @@
 # Verify ECDSA (secp256r1) signatures.
 sig-ecdsa = []
 
+# Verify ED25519 signatures.
+sig-ed25519 = []
+
 # Overwrite only upgrade
 overwrite-only = []