dt-bindings: rockchip: pmu: Narrow definition of reboot-mode

The 'reboot-mode' child of PMU node must be a syscon-reboot-mode one, so
add missing $ref to enforce the validation and disallow other
reboot-mode handlers.
Defining 'type: object' is on the other hand not necessary when other
schema is referenced.

This can be further restricted to match hardware/firmware:
syscon-reboot-mode schema allows arbitrary "mode-.* properties but only
a subset actually makes sense and is valid.  Provide negative look-ahead
pattern to disallow any modes not supported by the device, which
tightens the binding.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20260701105849.197086-3-krzysztof.kozlowski@oss.qualcomm.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

Documentation/devicetree/bindings/arm/rockchip/pmu.yaml

@@ -61,7 +61,13 @@ properties:
     type: object
 
   reboot-mode:
-    type: object
+    $ref: /schemas/power/reset/syscon-reboot-mode.yaml
+    unevaluatedProperties: false
+
+    patternProperties:
+      # Negative look-ahead to disallow unsupported modes. The '$' has to be
+      # part of lookahead group to work, instead of trailing outside of ().
+      "^mode-(?!(bootloader$|loader$|normal$|recovery$))": false
 
 required:
   - compatible