drm/i915/gt: Tidy up debug-warns for the mocs control table

As we always run new platforms through CI, we only need the debug code
compiled in during CI runs.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191112223600.30993-2-chris@chris-wilson.co.uk