drm/i915/gt: Pull timeline initialise to intel_gt_init_early

Our timelines are currently contained within an intel_gt, and we only
need to perform list/spinlock initialisation, so we can pull the
intel_timelines_init() into our intel_gt_init_early().

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191101130406.4142-1-chris@chris-wilson.co.uk