ARM: mxs: cfa10049: Add NAU7802 ADCs to the device tree

The Crystalfontz CFA-10049 has 3 Nuvoton NAU7802 ADCs, plugged behing a
GPIO-controlled I2C muxer because these ADCs don't have a configurable
address.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>