drm/i915/gem: Lazily acquire the device wakeref for freeing objects

We only need the device wakeref on freeing the objects if we have to
unbind the object from the global GTT, or otherwise update device
information. If the objects are clean, we never need the wakeref, so
avoid taking until required.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Reviewed-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200503171513.18704-1-chris@chris-wilson.co.uk