drm/i915/gem: Remove shared locking on freeing objects

The obj->base.resv may be shared across many objects, some of which may
still be live and locked, preventing objects from being freed
indefintely. We could individualise the lock during the free, or rely on
a freed object having no contention and being able to immediately free
the pages it owns.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/6469


Fixes: be7612fd ("drm/i915: Require object lock when freeing pages during destruction")
Fixes: 6cb12fbd ("drm/i915: Use trylock instead of blocking lock for __i915_gem_free_objects.")
Cc: <stable@vger.kernel.org> # v5.17+
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Nirmoy Das <nirmoy.das@intel.com>
Acked-by: Nirmoy Das <nirmoy.das@intel.com>
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220726144844.18429-1-nirmoy.das@intel.com