hwmon: Add a simple driver to read the MXS SoC temperature

The low resolution ADC of the mxs is able to read an internal temperature
sensor, expose that using hwmon.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
arm: mxs: Add mxs internal temp sensor to cfa-10036

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>