asn1: use the new symbol to guard dependencies of ECDSA conversion functions

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/include/mbedtls/asn1write.h b/include/mbedtls/asn1write.h
index 7af4aba..0c5a85a 100644
--- a/include/mbedtls/asn1write.h
+++ b/include/mbedtls/asn1write.h
@@ -36,7 +36,8 @@
 extern "C" {
 #endif
 
-#if defined(MBEDTLS_ASN1_WRITE_C) || defined(MBEDTLS_X509_USE_C)
+#if defined(MBEDTLS_ASN1_WRITE_C) || defined(MBEDTLS_X509_USE_C) || \
+    defined(MBEDTLS_PSA_UTIL_HAVE_ECDSA)
 /**
  * \brief           Write a length field in ASN.1 format.
  *
@@ -65,7 +66,7 @@
  */
 int mbedtls_asn1_write_tag(unsigned char **p, const unsigned char *start,
                            unsigned char tag);
-#endif /* MBEDTLS_ASN1_WRITE_C || MBEDTLS_X509_USE_C */
+#endif /* MBEDTLS_ASN1_WRITE_C || MBEDTLS_X509_USE_C || MBEDTLS_PSA_UTIL_HAVE_ECDSA*/
 
 #if defined(MBEDTLS_ASN1_WRITE_C)
 /**