Valgrind support

[Simon Richter]

Hi,

a few years ago I taught[1] Valgrind that DRM_IOCTL_I915_GEM_MMAP 
created accessible address space, so it would not complain about 
applications putting together command or vertex buffers.

I suspect that this is incomplete, because it doesn't handle unmapping, 
but IIRC also does not complain if the application does not unmap, and 
there might be other ioctls as well.

Updating this is on my to-do list, but at a fairly low priority, so it 
will probably be stuck there for a while, so if someone feels like they 
want to do something useful with a clearly defined scope and little 
future maintenance, consider this message an invitation to do so. :)

    Simon

[1] https://bugs.kde.org/show_bug.cgi?id=413119