mfd: Add support for TPS68470 device

The TPS68470 device is an advanced power management
unit that powers a Compact Camera Module (CCM),
generates clocks for image sensors, drives a dual
LED for Flash and incorporates two LED drivers for
general purpose indicators.

This patch adds support for TPS68470 mfd device.

Signed-off-by: Rajmohan Mani <rajmohan.mani@intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>