drm/i915/uc: Move intel functions to intel_uc

All the intel_uc_* can now be moved to work on the intel_uc structure
for better encapsulation of uc-related actions.

Note: I've introduced uc_to_gt instead of uc_to_i915 because the aim is
to move everything to be gt-focused in the medium term, so we would've
had to replace it soon anyway.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Acked-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190713100016.8026-8-chris@chris-wilson.co.uk
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>