QXL driver is used unconditionally

I see builds from the testing branch fail to start X, while previous versions worked just fine. It seems that due to the changes we introduced with #11500 (closed), the QXL driver is used in all cases, regardless of the actual hardware. I think we need to revert these changes for 2.4.

Related issues

Related to #11500 (closed)

Original created by @intrigeri on 11514 (Redmine)

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