[PATCH] Interface changes for prioritized contexts amd-staging-4.9

[Andres Rodriguez]

This patch has been rebased onto amd-staging-4.9.

It would be useful to have this patch outside the drm-next-4.12-wip branch as
it would unblock submission of the corresponding libdrm and mesa patches.

Splitting this off as it is my understanding that drm-next-4.12-wip may take a
while to land on drm-next due to some KIQ regressions.