Add milliseconds time function

We provide windows and posix implementation for it.
With MBEDTLS_PLATFORM_MS_TIME_ALT, user can provide
their own implementation.

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index d3c9a9f..18e6b56 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -454,6 +454,12 @@
 #error "MBEDTLS_PLATFORM_MS_TIME_TYPE_MACRO defined, but not all prerequisites"
 #endif
 
+#if defined(MBEDTLS_PLATFORM_MS_TIME_ALT)   && \
+    ( !defined(MBEDTLS_PLATFORM_C)          || \
+        !defined(MBEDTLS_HAVE_TIME) )
+#error "MBEDTLS_PLATFORM_MS_TIME_ALT defined, but not all prerequisites"
+#endif
+
 #if defined(MBEDTLS_PLATFORM_TIME_TYPE_MACRO) &&\
     ( !defined(MBEDTLS_PLATFORM_C) ||\
         !defined(MBEDTLS_HAVE_TIME) )