libcamera: Add SensorCropMaximum property

The SensorCropMaximum camera property reports the location of that
part of the image sensor array that can be scaled to produce the
output images, given in native sensor pixels. It will normally change
when a new camera mode is selected, and can be used to implement
digital zoom.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/libcamera/property_ids.yaml

@@ -663,4 +663,19 @@ controls:
         \todo Rename this property to ActiveAreas once we will have property
               categories (i.e. Properties::PixelArray::ActiveAreas)
 
+  - ScalerCropMaximum:
+      type: Rectangle
+      description: |
+        The maximum valid rectangle for the controls::ScalerCrop control. This
+        reflects the minimum mandatory cropping applied in the camera sensor and
+        the rest of the pipeline. Just as the ScalerCrop control, it defines a
+        rectangle taken from the sensor's active pixel array.
+
+        This property is valid only after the camera has been successfully
+        configured and its value may change whenever a new configuration is
+        applied.
+
+        \todo Turn this property into a "maximum control value" for the
+        ScalerCrop control once "dynamic" controls have been implemented.
+
 ...