Skip param validation tests if custom macro used

The test framework for validation of parameters depends on the macro
MBEDTLS_PARAM_FAILED() being set to its default value when building the
library. So far the test framework attempted to define this macro but this was
the wrong place - this definition wouldn't be picked by the library.

Instead, a different approach is taken: skip those tests when the macro is
defined in config.h, as in that case we have no way to know if it will indeed
end up calling mbedtls_param_failed() as we need it to.

This commit was tested by manually ensuring that aes_invalid_params:

- passes (and is not skipped) in the default configuration
- is skipped when MBEDTLS_PARAM_FAILED() is defined in config.h

tests/suites/test_suite_aes.function

@@ -371,7 +371,7 @@ exit:
 }
 /* END_CASE */
 
-/* BEGIN_CASE */
+/* BEGIN_CASE depends_on:MBEDTLS_CHECK_PARAMS:!MBEDTLS_PARAM_FAILED_ALT */
 void aes_invalid_param( )
 {
     mbedtls_aes_context dummy_ctx;