mfd: palmas PMIC device support

Palmas is a PMIC from Texas Instruments and this is the MFD part of the
driver for this chip. The PMIC has SMPS and LDO regulators, a general
purpose ADC, GPIO, USB OTG mode detection, watchdog and RTC features.
Signed-off-by: Graeme Gregory <gg@slimlogic.co.uk>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>