bootutil: Remove P224 curve

Signed-off-by: Roland Mikhel <roland.mikhel@arm.com>
Change-Id: I49fad7ede202de4e3c710bf4aa1df195a310b037
diff --git a/docs/design.md b/docs/design.md
index d1b7038..7a192cd 100755
--- a/docs/design.md
+++ b/docs/design.md
@@ -3,7 +3,7 @@
 
   - Copyright (c) 2017-2020 Linaro LTD
   - Copyright (c) 2017-2019 JUUL Labs
-  - Copyright (c) 2019-2021 Arm Limited
+  - Copyright (c) 2019-2023 Arm Limited
 
   - Original license:
 
@@ -107,7 +107,7 @@
 #define IMAGE_TLV_KEYHASH           0x01   /* hash of the public key */
 #define IMAGE_TLV_SHA256            0x10   /* SHA256 of image hdr and body */
 #define IMAGE_TLV_RSA2048_PSS       0x20   /* RSA2048 of hash output */
-#define IMAGE_TLV_ECDSA224          0x21   /* ECDSA of hash output */
+#define IMAGE_TLV_ECDSA224          0x21   /* ECDSA of hash output - Not supported anymore */
 #define IMAGE_TLV_ECDSA256          0x22   /* ECDSA of hash output */
 #define IMAGE_TLV_RSA3072_PSS       0x23   /* RSA3072 of hash output */
 #define IMAGE_TLV_ED25519           0x24   /* ED25519 of hash output */