Add missing include

Fix build failures with config full

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/tests/suites/test_suite_x509write.function b/tests/suites/test_suite_x509write.function
index c3b6768..ab4a2d0 100644
--- a/tests/suites/test_suite_x509write.function
+++ b/tests/suites/test_suite_x509write.function
@@ -7,6 +7,7 @@
 #include "mbedtls/rsa.h"
 #include "mbedtls/asn1write.h"
 #include "mbedtls/pk.h"
+#include "md_psa.h"
 
 #if defined(MBEDTLS_RSA_C)
 int mbedtls_rsa_decrypt_func(void *ctx, size_t *olen,