[Intel-gfx] Mika's reward

[Chris Wilson]

In preparation for relaxing the conditions under which we wait to allow
waiting on the GPU from any context (e.g. holding nearly any other
mutex) is to remove taking struct_mutex from inside GPU reset. The issue
being that any mutex required for GPU reset is required to avoid
indefinite waits while waiting on the GPU -- so any mutex on which we
wait, may not be used inside reset (or the shrinker). struct_mutex
circumvents this requirement by complicated recursion avoidance, a
lesson we do not want to repeat.
-chris