drm/i915/tgl: Add SFC instdone to error state

On debugging media workload hangs, sfc instdone
might prove useful in future. Be prepared.

Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20191029163841.5224-1-mika.kuoppala@linux.intel.com