drm/i915: Only dump GPU state on set-wedged if interesting

As we may frequently mark the device as wedged to flush requests off it
during the normal course of events, quite often we have a large state
dump that is of no interest. Don't bother dumping it all if the engines
are all idle.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190115122057.1677-1-chris@chris-wilson.co.uk