mfd: bd70528: Support ROHM bd70528 PMIC core

ROHM BD70528MWV is an ultra-low quiescent current general
purpose single-chip power management IC for battery-powered
portable devices.

Add MFD core which enables chip access for following subdevices:
	- regulators/LED drivers
	- battery-charger
	- gpios
	- 32.768kHz clk
	- RTC
	- watchdog

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>