configure: add option to allow building without evr support

Because of issue QTBUG-53019, the performance of an application playing a
video on windows is sometimes just a few fps. The issue seems to
be related to EVR on some hardware, and appeared in commit c7397523

.
This patch allows building the qtmultimedia module without EVR.

Task-number: QTBUG-53019
Change-Id: I1166e633dd02e93047fa72b0ac156ae615ab67ec
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>