drm/i915/selftests: Move uncore fw selftests to operate on intel_gt

Forcewake is the speciality of the GT, so it is natural to run the
intel_uncore_forcewake tests over the GT. So pass intel_gt as the
parameter to our selftests.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191022131016.9065-1-chris@chris-wilson.co.uk