drm/i915/guc: Add support for data reporting in GuC responses

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