mfd: max77686: Add Maxim 77802 PMIC support

Maxim MAX77802 is a power management chip that contains 10 high
efficiency Buck regulators, 32 Low-dropout (LDO) regulators used
to power up application processors and peripherals, a 2-channel
32kHz clock outputs, a Real-Time-Clock (RTC) and a I2C interface
to program the individual regulators, clocks outputs and the RTC.

This patch adds support for MAX77802 to the MAX77686 driver and is
based on a driver added to the Chrome OS kernel 3.8 by Simon Glass.

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>