drm/i915/guc: Move GuC core definitions into dedicated files

Move GuC core definitions into dedicated files as we want to
keep GuC specific code in separated files.

v2: move all functions in single patch (Joonas)
    fix old checkpatch issues (Sagar)

v3: rebased

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Reviewed-by: Sagar Arun Kamble <sagar.a.kamble@intel.com> #1
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171004181343.66348-4-michal.wajdeczko@intel.com