libcamera: controls: Handle enum values without a cast

When constructing a ControlValue from an enum value, an explicit cast to
int32_t is needed as we use int32_t as the underlying type for all
enumerated controls. This makes users of ControlValue more complex. To
simplify them, specialize the control_type template for enum types, to
support construction of ControlValue directly without a cast.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/pipeline/ipu3/ipu3.cpp

@@ -958,7 +958,7 @@ int PipelineHandlerIPU3::updateControls(IPU3CameraData *data)
 		values.reserve(testPatternModes.size());
 
 		for (auto pattern : testPatternModes)
-			values.emplace_back(static_cast<int32_t>(pattern));
+			values.emplace_back(pattern);
 
 		controls[&controls::draft::TestPatternMode] = ControlInfo(values);
 	}