drm/i915/uc: move GuC/HuC inside intel_gt under a new intel_uc

Being part of the GT HW, it make sense to keep the guc/huc structures
inside the GT structure. To help with the encapsulation work done by the
following patches, both structures are placed inside a new intel_uc
container. Although this results in code with ugly nested dereferences
(i915->gt.uc.guc...), it saves us the extra work required in moving
the structures twice (i915 -> gt -> uc). The following patches will
reduce the number of places where we try to access the guc/huc
structures directly from i915 and reduce the ugliness.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190713100016.8026-7-chris@chris-wilson.co.uk
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>