drm/i915: Reboot CI if forcewake fails

If the HW fails to ack a change in forcewake status, the machine is as
good as dead -- it may recover, but in reality it missed the mmio
updates and is now in a very inconsistent state. If it happens, we can't
trust the CI results (or at least the fails may be genuine but due to
the HW being dead and not the actual test!) so reboot the machine (CI
checks for a kernel taint in between each test and reboots if the
machine is tainted).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190508115245.27790-1-chris@chris-wilson.co.uk