drm/i915: Show the GPU state when declaring wedged

Dump each engine state when i915_gem_set_wedged() is called to give us
some more clues as to why we had to terminate the GPU.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180205092201.19476-5-chris@chris-wilson.co.uk