meson: switch config.h to config.hpp

Enable a transition of this file from C to C++ so that we
can use C++ constants instead of #defines in future commits.

Change-Id: I1149ebdaaeb99b7e7974ca846b9b07a3399edea0
Signed-off-by: Delphine CC Chiu <Delphine_CC_Chiu@wiwynn.com>
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/src/host_then_chassis_poweroff.cpp b/src/host_then_chassis_poweroff.cpp
index 5aedc9f..7abde43 100644
--- a/src/host_then_chassis_poweroff.cpp
+++ b/src/host_then_chassis_poweroff.cpp
@@ -1,7 +1,6 @@
-#include "config.h"
-
 #include "host_then_chassis_poweroff.hpp"
 
+#include "config.hpp"
 #include "power_button_profile_factory.hpp"
 
 #include <phosphor-logging/lg2.hpp>