bootutil: Remove curve specific ECDSA TLVs

Remove those TLVs that are tied to a specific curve and update
the image validation logic to look for the new generic TLV

Signed-off-by: Roland Mikhel <roland.mikhel@arm.com>
Change-Id: I924f2742424bc255fbed1b0941648baa88f60147
diff --git a/docs/design.md b/docs/design.md
index 7a192cd..12d68ee 100755
--- a/docs/design.md
+++ b/docs/design.md
@@ -108,9 +108,10 @@
 #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 - Not supported anymore */
-#define IMAGE_TLV_ECDSA256          0x22   /* ECDSA of hash output */
+#define IMAGE_TLV_ECDSA256          0x22   /* ECDSA of hash output - Not supported anymore */
 #define IMAGE_TLV_RSA3072_PSS       0x23   /* RSA3072 of hash output */
 #define IMAGE_TLV_ED25519           0x24   /* ED25519 of hash output */
+#define IMAGE_TLV_ECDSA_SIG         0x25   /* ECDSA of hash output */
 #define IMAGE_TLV_ENC_RSA2048       0x30   /* Key encrypted with RSA-OAEP-2048 */
 #define IMAGE_TLV_ENC_KW            0x31   /* Key encrypted with AES-KW-128 or
                                               256 */