drm/i915/guc: Keep strict GuC ABI definitions

Our fwif.h file is now mix of strict firmware ABI definitions and
set of our helpers. In anticipation of upcoming changes to the GuC
interface try to keep them separate in smaller maintainable files.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210603051630.2635-6-matthew.brost@intel.com