drm/i915: Break up long runs of freeing objects

drm/i915: Break up long runs of freeing objects

Before freeing the next batch of objects from the worker, check if the
worker's timeslice has expired and if so, defer the next batch to the
next invocation of the worker.

Suggested-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170407102552.5781-3-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>