iio: accel: bmc150-accel: Add rudimentary regulator support

These Bosch accelerometers have two supplies, VDD and VDDIO.
Add some rudimentary support to obtain and enable these
regulators during probe() and disable them during remove()
or on the errorpath.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20201115205745.618455-3-linus.walleij@linaro.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>