Split QMediaRecorder::setEncodingSettings to separate setters.

Split QMediaRecorder::setEncodingSettings to separate setters.

It's easier to change only the necessary part of encoding settings.
The settings are applied during the next event loop or before recording
starts.

Change-Id: Ia2b5c93826a302212aa7f79a0c75e4cbaaf1dd7a
Reviewed-by: Ling Hu <ling.hu@nokia.com>
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>