controls: rpi: Add ControlId control

The ControlId identifies the list of controls that have been applied
to the images in this request for the first time. The controls must
have been submitted to the camera system using Camera::queueControls.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>

Author: davidplowman

src/libcamera/control_ids_rpi.yaml

@@ -299,4 +299,21 @@ controls:
         This control returns performance metrics for the CNN processing stage.
         Two values are returned in this span, the runtime of the CNN/DNN stage
         and the DSP stage in milliseconds.
+
+  - ControlId:
+      type: int64_t
+      direction: out
+      description: |
+        This is the control list id number that is synchonised with this
+        request, meaning that this request is the first one where the images
+        have had the identified list of controls applied.
+
+        Every time a control list is queued using Camera::queueControls, it
+        is assigned a new sequence number, starting at 1 on the first such
+        after the camera is started, and increasing by one on every subsequent
+        call.
+
+        This is the number that is then reported back as the ControlId. When
+        no controls have been sent with Camera::queueControls, the ControlId
+        reports the value zero.
 ...