doc: build: dts: api: document the zephyr,camera chosen node

The zephyr,camera was used in several samples, but was not documented.
Add the missing documentation entry for it in the list.

Signed-off-by: Josuah Demangeon <me@josuah.net>

doc/build/dts/api/api.rst

@@ -388,6 +388,8 @@ device.
      - Sets UART device used for the Bluetooth monitor logging
    * - zephyr,bt-hci
      - Selects the HCI device used by the Bluetooth host stack
+   * - zephyr,camera
+     - Video input device, typically a camera.
    * - zephyr,canbus
      - Sets the default CAN controller
    * - zephyr,ccm