drm/i915: Pass i915_sched_node around internally

To simplify the next patch, update bump_priority and schedule to accept
the internal i915_sched_ndoe directly and not expect a request pointer.

add/remove: 0/0 grow/shrink: 2/1 up/down: 8/-15 (-7)
Function                                     old     new   delta
i915_schedule_bump_priority                  109     113      +4
i915_schedule                                 50      54      +4
__i915_schedule                              922     907     -15

v2: Adopt node for the old rq local, since it no longer is a request but
the origin node.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190513120102.29660-2-chris@chris-wilson.co.uk