iio: light: ltr501: Add rudimentary regulator support

On some platforms the supply regulators must be enabled before the
sensor can work. Add vdd and vddio regulators for the sensor and IO bus
power respectively.

Signed-off-by: Nikita Travkin <nikita@trvn.ru>
Link: https://lore.kernel.org/r/20211006163058.145842-3-nikita@trvn.ru


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