ANGLE: Enable D3D11 for feature level 9 cards

Enable use of ANGLE on lower-end hardware, such as Surface RT and
Windows Phone 8.

Based on https://codereview.appspot.com/12917046/

Change-Id: Ice536802e4eedc1d264abd0dd65960638fce59e4
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>