[Intel-gfx] Sleepless per-engine resests

[Chris Wilson]

The original goal for per-engine reset was to allow them from irq
context for the purpose of implementing a fast watchdog. However, since
we haven't been using them from even softirq context, we have
accumulated a number of sleeps and synchronous waits. With the desire
for a fast reset to unblock preemption, let's resetting from an atomic
context again.
-Chris