drm/i915: Display current hangcheck status in debugfs

drm/i915: Display current hangcheck status in debugfs

For example,

/sys/kernel/debug/dri/0/i915_hangcheck_info:

Hangcheck active, fires in 15887800ms
render ring:
        seqno = -4059 [current -583]
        action = 2
        score = 0
        ACTHD = 1ee8 [current 21f980]
        max ACTHD = 0

v2: Include expiration ETA. Can anyone spot a problem?
v3: Convert for workqueued hangcheck (Mika)
v4: Print seqnos as unsigned ints (Ville)
v5: Print seqnos as hex (Chris)

Tested-By: PRC QA PRTS (Patch Regression Test System Contact: shuang.he@intel.com) (v2)
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> (v2)
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>