hwmon: Add Freescale MC13783 ADC driver

This driver provides support for the ADC integrated into the
Freescale MC13783 PMIC.

Signed-off-by: Luotao Fu <l.fu@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Cc: Eric Piel <eric.piel@tremplin-utc.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>