misc fixes on virtio-gpu-next

The first 6 patches are small patches mainly fixing comments. Feel free to squash them in the tree before posting upstream.

The last 2 are more complex, the way context initialization change and it was quite a problem on back compat on current virgl context. @gurchetansingh can you explain why this change and why the setparam capability is comment ? I don't see any other parameter than capset setting, can you give me an example of any useful parameter to set ?