drm/i915: Drop i915_gem_obj_is_pinned() from set-cache-level

drm/i915: Drop i915_gem_obj_is_pinned() from set-cache-level

Since the remove of the pin-ioctl, we only care about not changing the
cache level on buffers pinned to the hardware as indicated by
obj->pin_display. By knowing that only objects pinned to the hardware
will have an elevated vma->pin_count, so we can coallesce many of the
linear walks over the obj->vma_list.

v2: Try and retrospectively add comments explaining the steps in
rebinding the active VMA.

Signed-off-by: Chris Wilson <[email protected]>
Cc: Tvrtko Ursulin <[email protected]>
Reviewed-by: Tvrtko Ursulin <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>