dts: Include devicetree.h instead of generated_dts_board.h

Needed for https://github.com/zephyrproject-rtos/zephyr/pull/20757, to
avoid a warning-turned-error.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>
diff --git a/boot/zephyr/include/sysflash/sysflash.h b/boot/zephyr/include/sysflash/sysflash.h
index 25487ee..e745ffa 100644
--- a/boot/zephyr/include/sysflash/sysflash.h
+++ b/boot/zephyr/include/sysflash/sysflash.h
@@ -3,7 +3,7 @@
 #ifndef __SYSFLASH_H__
 #define __SYSFLASH_H__
 
-#include <generated_dts_board.h>
+#include <devicetree.h>
 #include <mcuboot_config/mcuboot_config.h>
 
 #if (MCUBOOT_IMAGE_NUMBER == 1)