On some STMicroelectronics hardware reside regulators consisting
partly of a PWM input connected to the feedback loop. As the PWM
duty-cycle is varied the output voltage adapts. This driver
allows us to vary the output voltage by adapting the PWM input
duty-cycle.
Signed-off-by: NLee Jones <lee.jones@linaro.org>
Signed-off-by: NMark Brown <broonie@linaro.org>