iio: magnetometer: bmc150: Add rudimentary regulator support

iio: magnetometer: bmc150: Add rudimentary regulator support

BMC150 needs VDD and VDDIO regulators that might need to be explicitly
enabled. Add some rudimentary support to obtain and enable these
regulators during probe() and disable them during remove()
or on the error path.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20210109152327.512538-2-stephan@gerhold.net
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>