drm/i915: extract some common olr+wedge code

The new wait_rendering ioctl also needs to check for an oustanding
lazy request, and we already duplicate that logic at three places. So
extract it.

While at it, also extract the code to check the gpu wedging state to
improve code flow.

v2: Don't use seqno as an outparam (Chris)

v3 by danvet: Kill stale comment and pimp commit message

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