ipa: raspberrypi: AWB: Fix race condition setting manual gains

Applying the manual_r_ and manual_b_ values is entirely removed from
the asynchronous thread where their use constituted a race hazard. The
main thread now deals with them entirely, involving the following
changes.

1. SetManualGains() applies the new values directly to the
"sync_results", meaning that Prepare() will jump to the new values
immediately (which is a better behaviour).

2. Process() does not restart the asynchronous thread when manual
gains are in force.

3. The asynchronous thread might be running when manual gains are set,
so we ignore the results produced in this case.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/ipa/raspberrypi/controller/rpi/awb.hpp

@@ -108,6 +108,7 @@ public:
 	};
 
 private:
+	bool isAutoEnabled() const;
 	// configuration is read-only, and available to both threads
 	AwbConfig config_;
 	std::thread async_thread_;