GuC may return additional data in the response message.
Format and meaning of this data is action specific. We will
use this non-negative data as a new success return value.
Currently used actions don't return data that way yet.

v2: fix prohibited space after '~' (Michel)
    update commit message (Daniele)
v3: rebase
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Michel Thierry <michel.thierry@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180326194829.58836-3-michal.wajdeczko@intel.com