iio: Reconcile operation order between iio_register/unregister and pm functions

At probe, runtime pm should be setup before registering the sysfs interface so
that all the power attributes are accurate and functional when registering.
Also, when removing the device we should unregister first to make sure
that the interfaces that may result in wakeups are no longer available.

Fix this behaviour for the following drivers: bmc150, bmg160, kmx61,
kxcj-1013, mma9551, mma9553, rpr0521.

Signed-off-by: Adriana Reus <adriana.reus@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>