ecp_curves: Introduced `mbedtls_ecp_mod_p224k1()`

This patch introduces a `MBEDTLS_STATIC_TESTABLE` helper
method which exposes `ecp_mod_p256k1()` to the test-framework

Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
diff --git a/library/ecp_invasive.h b/library/ecp_invasive.h
index ae8598d..b7cd6e2 100644
--- a/library/ecp_invasive.h
+++ b/library/ecp_invasive.h
@@ -182,7 +182,7 @@
 #if defined(MBEDTLS_ECP_DP_SECP224K1_ENABLED)
 
 MBEDTLS_STATIC_TESTABLE
-int ecp_mod_p224k1(mbedtls_mpi *N);
+int mbedtls_ecp_mod_p224k1(mbedtls_mpi *N);
 
 #endif /* MBEDTLS_ECP_DP_SECP224K1_ENABLED */