arm64: dts: rockchip: add header for RK8XX PMIC constants

To make it easier to read the device tree, let's add constants for the
rockchip,reset-mode property values that are currently only applicable
to RK806 PMIC.

Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
[dt-maintainers did not consider this part of the binding, so we're
 keeping the header in the devicetree directory]
Link: https://lore.kernel.org/r/20250627-rk8xx-rst-fun-v4-3-ce05d041b45f@cherry.de
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

Author: QSchulz

arch/arm64/boot/dts/rockchip/rk8xx.h

@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: (GPL-2.0-or-later OR MIT) */
+/*
+ * Device Tree defines for Rockchip RK8xx PMICs
+ *
+ * Copyright 2025 Cherry Embedded Solutions GmbH
+ *
+ * Author: Quentin Schulz <quentin.schulz@cherry.de>
+ */
+
+#ifndef _DT_MFD_ROCKCHIP_RK8XX_H
+#define _DT_MFD_ROCKCHIP_RK8XX_H
+
+/* For use with rockchip,reset-mode property */
+#define RK806_RESTART		0
+#define RK806_RESET		1
+#define RK806_RESET_NOTIFY	2
+
+#endif