Reuse existing code from the WMF plugin, which already uses the EVR.
This enables HW-accelerated video decoding when using QMediaPlayer
with a QVideoWidget.

Task-number: QTBUG-45593
Change-Id: I757e4d53cd2c648aee6ba33a4851a8c6adc62843
Reviewed-by: Christian Stromme <christian.stromme@theqtcompany.com>