Add std PRI macro for printing milliseconds

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/include/mbedtls/platform_time.h b/include/mbedtls/platform_time.h
index 3158e2a..c7973d9 100644
--- a/include/mbedtls/platform_time.h
+++ b/include/mbedtls/platform_time.h
@@ -43,6 +43,7 @@
 typedef MBEDTLS_PLATFORM_MS_TIME_TYPE_MACRO mbedtls_ms_time_t;
 #else
 #include <stdint.h>
+#include <inttypes.h>
 typedef int64_t mbedtls_ms_time_t;
 #endif /* MBEDTLS_PLATFORM_MS_TIME_TYPE_MACRO */