Use correct offset for gpiochip0 on flat

Until kernel version 6.6 the first gpio chip's offset started at 0 due to a
downstream patch of RPi. This patch was removed with 6.6 and the kernel now
follows the mainline behavior whereas the offset starts as 512 ([1]).

Unfortunately we rely on indexed gpio access in revpi_flat.c for the relay
and button, as there is no platform device we can query. Thus keep the
current implementation at least for now and add a version macro, which
takes care of the offset calculation.

[1] raspberrypi/linux#6037 (comment)

Signed-off-by: Nicolai Buchwitz <n.buchwitz@kunbus.com>

src/revpi_flat.c

@@ -15,19 +15,27 @@
 #include <linux/sched.h>
 #include <linux/thermal.h>
 #include <linux/types.h>
+#include <linux/version.h>
 
 #include "piControlMain.h"
 #include "process_image.h"
 #include "revpi_common.h"
 #include "revpi_flat.h"
 #include "RevPiDevice.h"
 
+#if KERNEL_VERSION(6, 6, 0) > LINUX_VERSION_CODE
+/* kernel before 6.6 has a custom RPi patch, so offset started at 0 */
+#define GPIOCHIP0_OFFSET	0
+#else
+#define GPIOCHIP0_OFFSET	512
+#endif
+
 /* relais gpio num */
-#define REVPI_FLAT_RELAIS_GPIO			28
+#define REVPI_FLAT_RELAIS_GPIO			(28 + GPIOCHIP0_OFFSET)
 
 /* button gpio num */
-#define REVPI_FLAT_BUTTON_GPIO			13
-#define REVPI_FLAT_S_BUTTON_GPIO		23
+#define REVPI_FLAT_BUTTON_GPIO			(13 + GPIOCHIP0_OFFSET)
+#define REVPI_FLAT_S_BUTTON_GPIO		(23 + GPIOCHIP0_OFFSET)
 
 #define REVPI_FLAT_DOUT_THREAD_PRIO		(MAX_RT_PRIO / 2 + 8)
 #define REVPI_FLAT_AIN_THREAD_PRIO		(MAX_RT_PRIO / 2 + 6)