meson: Remove -Wno-unused-parameter

We build libcamera with -Wno-unused-parameter and this doesn't cause
much issue internally. However, it prevents catching unused parameters
in inline functions defined in public headers. This can lead to
compilation warnings for applications compiled without
-Wno-unused-parameter.

To catch those issues, remove -Wno-unused-parameter and fix all the
related warnings with [[maybe_unused]].

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/ipa/raspberrypi/controller/rpi/agc.cpp

@@ -221,7 +221,8 @@ void Agc::SetConstraintMode(std::string const &constraint_mode_name)
 	constraint_mode_name_ = constraint_mode_name;
 }
 
-void Agc::SwitchMode(CameraMode const &camera_mode, Metadata *metadata)
+void Agc::SwitchMode([[maybe_unused]] CameraMode const &camera_mode,
+		     Metadata *metadata)
 {
 	// On a mode switch, it's possible the exposure profile could change,
 	// so we run through the dividing up of exposure/gain again and