[PATCH v2] High priority usermode contexts

[Andres Rodriguez]

This patch series provides the initial APIs for high priority contexts.

The current implementation is based on top of the SW scheduler, there
are no HW priorities set yet.

This doesn't provide the quality of service we need for VR. Further changes
to enable HW priorities will be required.

For some performance data collected with multiple apps see:
https://lists.freedesktop.org/archives/amd-gfx/2016-December/004257.html

Test apps available here:
https://github.com/lostgoat/Vulkan

Related libdrm/radv patches to follow