iio: vcnl4000: Enable runtime pm for vcnl4200/4040

This is modelled after the vcnl4035 driver. For the vcnl40{0,1,2}0
we don't do anything since they use on demand measurement.

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>