lib: Add support for ECDSA image signing

mkimage supports rsa2048, and rsa4096 signatures. With newer silicon
now supporting hardware-accelerated ECDSA, it makes sense to expand
signing support to elliptic curves.

Implement host-side ECDSA signing and verification with libcrypto.
Device-side implementation of signature verification is beyond the
scope of this patch.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/common/image-sig.c b/common/image-sig.c
index 54f0eb2..0f8e592 100644
--- a/common/image-sig.c
+++ b/common/image-sig.c
@@ -16,6 +16,7 @@
 DECLARE_GLOBAL_DATA_PTR;
 #endif /* !USE_HOSTCC*/
 #include <image.h>
+#include <u-boot/ecdsa.h>
 #include <u-boot/rsa.h>
 #include <u-boot/hash-checksum.h>
 
@@ -83,8 +84,14 @@
 		.sign = rsa_sign,
 		.add_verify_data = rsa_add_verify_data,
 		.verify = rsa_verify,
-	}
-
+	},
+	{
+		.name = "ecdsa256",
+		.key_len = ECDSA256_BYTES,
+		.sign = ecdsa_sign,
+		.add_verify_data = ecdsa_add_verify_data,
+		.verify = ecdsa_verify,
+	},
 };
 
 struct padding_algo padding_algos[] = {