drm/i915: Remove irq-related FIXME in reset code

With the two-step reset counter increments which braket the actual
reset code and the subsequent wake-up we're guaranteeing that all the
lockless waiters _will_ be woken up. And since we unconditionally bail
out of waits with -EAGAIN (or -EIO) in that case there is not risk of
lost interrupt enabling bits when the lockless wait code races against
a gpu reset.

Let's remove this FIXME as resolved then.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>