drm/i915: save/restore interrupt state

On resume, if the interrupt state isn't restored correctly, we may end
up with a flood of unexpected or ill-timed interrupts, which could cause
the kernel to disable the interrupt or vblank events to happen at the
wrong time.  So save/restore them properly.

Signed-off-by: Dave Airlie <airlied@linux.ie>

diff --cc drivers/char/drm/i915_drv.c
Simple merge

diff --cc drivers/char/drm/i915_drv.h
Simple merge