drm/i915: Move i915_gem_chipset_flush to intel_gt

This aligns better with the rest of restructuring.

v2:
 * Move call out of line. (Chris)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190621070811.7006-24-tvrtko.ursulin@linux.intel.com
12 files changed