drm/i915/guc: Trace messages from CT while in debug

During debug we may want to investigate all communication
from the Guc. Add proper tracing macros in debug config.

v2: convert remaining DRM_DEBUG into new CT_DEBUG (Michal)
v3: use dedicated Kconfig (Daniele)
v4: checkpatch

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>
Acked-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180326194829.58836-12-michal.wajdeczko@intel.com