drm/i915: Add error code into error state

commit 011cf577
Author: Ben Widawsky <benjamin.widawsky@intel.com>
Date:   Tue Feb 4 12:18:55 2014 +0000

    drm/i915: Generate a hang error code

added error code debug into dmesg. Store this also
with error state to make matching dmesg logs and error
states easier.

As we need to have full ring state for error code generation,
do full capture always, print hang message into log and then
decide if we need to keep the error state.

Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>