drm/i915/uc: Log fw status changes only under debug config

We don't care about internal firmware status changes unless
we are doing some real debugging. Note that our CI is not
using DRM_I915_DEBUG_GUC config by default so use it.

v2: protect against accidental overwrites (Chris)

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
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/20190813081559.23936-1-michal.wajdeczko@intel.com