Sort out MD dependencies in RSA tests

When MD is only used to compute a size, use md_internal.h instead.

When it's actually used to compute a hash, mark the test function as
depending on it. This is probably suboptimal in the long run, and we
might want to either adapt the code so that it can use PSA Crypto
instead, or just pre-compute the hash in the test data.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/tests/suites/test_suite_pkcs1_v15.function b/tests/suites/test_suite_pkcs1_v15.function
index 6f859d5..00da294 100644
--- a/tests/suites/test_suite_pkcs1_v15.function
+++ b/tests/suites/test_suite_pkcs1_v15.function
@@ -261,7 +261,7 @@
 }
 /* END_CASE */
 
-/* BEGIN_CASE */
+/* BEGIN_CASE depends_on:MBEDTLS_MD_C */
 void pkcs1_rsassa_v15_sign( int mod, int radix_P, char * input_P, int radix_Q,
                             char * input_Q, int radix_N, char * input_N,
                             int radix_E, char * input_E, int digest, int hash,
@@ -320,7 +320,7 @@
 }
 /* END_CASE */
 
-/* BEGIN_CASE */
+/* BEGIN_CASE depends_on:MBEDTLS_MD_C */
 void pkcs1_rsassa_v15_verify( int mod, int radix_N, char * input_N,
                               int radix_E, char * input_E, int digest,
                               int hash, data_t * message_str, char * salt,