MFXVideoDecode_Init() fails with MFX_ERR_UNSUPPORTED

When I call MFXVideoDecode_Init() it fails with MFX_ERR_UNSUPPORTED. 

I'm using an annex-b .h264 file that I generated with FFMPEG. I get the same error when I use the .264 file from the samples; this is obvious ofcourse as VideoDECODEH264::Init() has a #ifdef that triggers the return of MFX_ERR_UNSUPPORTED, as you can see in the linked code

VideoDECODEH264::Init() returns MFX_ERR_UNSUPPORTED because MFX_VA_LINUX is defined in mfx_config.h:

 But I wasn't able to find where MFX_VA was defined.

How can I fix this?

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