doc: devicetree: Add zephyr,settings-partition to list of available chosens

Add newly added chosen to the list to keep it complete.

Signed-off-by: Alexander Mihajlovic <a@abxy.se>
diff --git a/doc/reference/devicetree/api.rst b/doc/reference/devicetree/api.rst
index 03f14f26..2c4630c 100644
--- a/doc/reference/devicetree/api.rst
+++ b/doc/reference/devicetree/api.rst
@@ -411,6 +411,9 @@
      - Used by the OpenThread to specify UART device for Spinel protocol
    * - zephyr,pcie-controller
      - The node corresponding to the PCIe Controller
+   * - zephyr,settings-partition
+     - Fixed partition node. If defined this selects the partition used
+       by the NVS and FCB settings backends.
    * - zephyr,shell-uart
      - Sets UART device used by serial shell backend
    * - zephyr,sram