This change converts the driver to register via devm_iio_device_register().
For the tmp006_powerdown() hook, this uses a devm_add_action() hook to put
the device in powerdown mode when it's unregistered.

With these changes, the remove hook can be removed.

The i2c_set_clientdata() call is staying around as the private data is used
in the PM routines.
Signed-off-by: Alexandru Ardelean <aardelean@deviqon.com>
Link: https://lore.kernel.org/r/20210624081924.15897-1-aardelean@deviqon.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>