drm/i915: Trylock the object when shrinking

We're working on requiring the obj->resv lock during unbind, fix
the shrinker to take the object lock.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211216142749.1966107-10-maarten.lankhorst@linux.intel.com