test: add a companion test for another curve (x25519) and fix issues

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/tests/suites/test_suite_ecp.function b/tests/suites/test_suite_ecp.function
index 2bf1904..9faeef5 100644
--- a/tests/suites/test_suite_ecp.function
+++ b/tests/suites/test_suite_ecp.function
@@ -1301,7 +1301,7 @@
 }
 /* END_CASE */
 
-/* BEGIN_CASE depends_on:MBEDTLS_TEST_HOOKS */
+/* BEGIN_CASE depends_on:MBEDTLS_TEST_HOOKS:MBEDTLS_ECP_DP_SECP192R1_ENABLED */
 void ecp_mod_p192_raw(char *input_N,
                       char *input_X,
                       char *result)