drm/i915/gt: Call intel_gt_sanitize() directly

Assume all responsibility for operating on the HW to sanitize the GT
state upon load/resume in intel_gt_sanitize() itself.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191101141009.15581-1-chris@chris-wilson.co.uk