iesce the GPU before disabling interrupts
and so the atomic polling should never occur.

This was recommended by Chris Wilson as a way of reducing added
complexity to the polled wait which I introduced in an RFC patch.

09:57 < ickle_> it's only there as a fudge for waiting after irqs
after uninstalled during s&r, we aren't actually meant to hit it
09:57 < ickle_> so maybe we should just kill the code there and fix the breakage

v2: return -ENODEV instead of -EBUSY when irq_get fails

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
…