Fix ecp_muladd test cases never getting executed

These test cases had been backported from Mbed TLS 2.x with a dependency
symbol that didn't exist in 2.16. Declare that symbol.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/test_suite_ecp.function b/tests/suites/test_suite_ecp.function
index 9c90e9c..3e901f7 100644
--- a/tests/suites/test_suite_ecp.function
+++ b/tests/suites/test_suite_ecp.function
@@ -1,6 +1,25 @@
 /* BEGIN_HEADER */
 #include "mbedtls/ecp.h"
 
+/* Backported from Mbed TLS 2.x for test dependencies. */
+#if defined(MBEDTLS_ECP_DP_SECP192R1_ENABLED) || \
+    defined(MBEDTLS_ECP_DP_SECP224R1_ENABLED) || \
+    defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED) || \
+    defined(MBEDTLS_ECP_DP_SECP384R1_ENABLED) || \
+    defined(MBEDTLS_ECP_DP_SECP521R1_ENABLED) || \
+    defined(MBEDTLS_ECP_DP_BP256R1_ENABLED) || \
+    defined(MBEDTLS_ECP_DP_BP384R1_ENABLED) || \
+    defined(MBEDTLS_ECP_DP_BP512R1_ENABLED) || \
+    defined(MBEDTLS_ECP_DP_SECP192K1_ENABLED) || \
+    defined(MBEDTLS_ECP_DP_SECP224K1_ENABLED) || \
+    defined(MBEDTLS_ECP_DP_SECP256K1_ENABLED)
+#define MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED
+#endif
+#if defined(MBEDTLS_ECP_DP_CURVE25519_ENABLED) || \
+    defined(MBEDTLS_ECP_DP_CURVE448_ENABLED)
+#define MBEDTLS_ECP_MONTGOMERY_ENABLED
+#endif
+
 #define ECP_PF_UNKNOWN     -1
 
 #define ECP_PT_RESET( x )           \