psa: Enable testing RSA decryption with output sizes

For must-fail asymmetric decryption tests, add an output size parameter
so that tests can directly control what output buffer size they allocate
and use independently from the key size used. This enables better
testing of behavior with various output buffer sizes.
diff --git a/tests/suites/test_suite_psa_crypto.function b/tests/suites/test_suite_psa_crypto.function
index 8b0b839..2a49141 100644
--- a/tests/suites/test_suite_psa_crypto.function
+++ b/tests/suites/test_suite_psa_crypto.function
@@ -3258,19 +3258,19 @@
                               int alg_arg,
                               data_t *input_data,
                               data_t *label,
+                              int output_size_arg,
                               int expected_status_arg  )
 {
     psa_key_handle_t handle = 0;
     psa_key_type_t key_type = key_type_arg;
     psa_algorithm_t alg = alg_arg;
     unsigned char *output = NULL;
-    size_t output_size = 0;
+    size_t output_size = output_size_arg;
     size_t output_length = ~0;
     psa_status_t actual_status;
     psa_status_t expected_status = expected_status_arg;
     psa_key_policy_t policy = PSA_KEY_POLICY_INIT;
 
-    output_size = key_data->len;
     ASSERT_ALLOC( output, output_size );
 
     PSA_ASSERT( psa_crypto_init( ) );