The new Khadas VIM2 and VIM3 boards controls the cooling fan via the
on-board microcontroller.

This implements the FAN control as thermal devices and as cell of the Khadas
MCU MFD driver.
Signed-off-by: NNeil Armstrong <narmstrong@baylibre.com>
Reviewed-by: NAmit Kucheria <amit.kucheria@linaro.org>
Acked-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: NLee Jones <lee.jones@linaro.org>