mfd: twl4030-madc: Add DT support and convert to IIO framework

This converts twl4030-madc module to use the Industrial IO ADC
framework and adds device tree support.

Signed-off-by: Sebastian Reichel <sre@debian.org>
Tested-by: Marek Belisko <marek@goldelico.com>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>