Add missing include of stdio.h

This is required in util.h in PSASIM as it uses fprintf. Previously
stdio was inadvertantly included via psa/crypto_struct.h (of all
places).

Signed-off-by: David Horstmann <david.horstmann@arm.com>

tests/psa-client-server/psasim/include/util.h

@@ -7,6 +7,8 @@
 
 #include "service.h"
 
+#include <stdio.h>
+
 #define PRINT(fmt, ...) \
     fprintf(stdout, fmt "\n", ##__VA_ARGS__)