mb/siemens/chili: Introduce include folder for header files

Use include folder for header files allowing proper includes.

Change-Id: I80066fb925b918d040062397e633c5d499a50dbe
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47973
Reviewed-by: Michael Niewöhner <foss@mniewoehner.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/mainboard/siemens/chili/romstage.c b/src/mainboard/siemens/chili/romstage.c
index c1ec7e4..a981f50 100644
--- a/src/mainboard/siemens/chili/romstage.c
+++ b/src/mainboard/siemens/chili/romstage.c
@@ -4,8 +4,7 @@
 #include <soc/cnl_memcfg_init.h>
 #include <soc/gpio.h>
 #include <soc/romstage.h>
-
-#include "variant.h"
+#include <variant.h>
 
 static void mainboard_init(void)
 {