ipa: raspberry: awb: Include <functional>

Building on gcc8 on Debian 10 fails with

 asyncThread_ = std::thread(std::bind(&Awb::asyncFunc, this));
../src/ipa/raspberrypi/controller/rpi/awb.cpp:177:34: note: ‘std::bind’
is defined in header ‘<functional>’; did you forget to ‘#include
<functional>’?

Fix that by including <functional> in awb.cpp.

Fixes: c1597f9896 ("ipa: raspberrypi: Use YamlParser to replace dependency on boost")
Reported-by: https://buildbot.libcamera.org/#/builders/6/builds/414
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>

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

@@ -6,6 +6,7 @@
  */
 
 #include <assert.h>
+#include <functional>
 
 #include <libcamera/base/log.h>