Add ecdsa signing support to the simulator

Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/sim/src/lib.rs b/sim/src/lib.rs
index 1314c42..b83e31b 100644
--- a/sim/src/lib.rs
+++ b/sim/src/lib.rs
@@ -887,7 +887,13 @@
     TlvGen::new_rsa_pss()
 }
 
+#[cfg(feature = "sig-ecdsa")]
+fn make_tlv() -> TlvGen {
+    TlvGen::new_ecdsa()
+}
+
 #[cfg(not(feature = "sig-rsa"))]
+#[cfg(not(feature = "sig-ecdsa"))]
 fn make_tlv() -> TlvGen {
     TlvGen::new_hash_only()
 }