mfd: Add new mfd device for TPS65217

The TPS65217 chip is a power management IC for Portable Navigation Systems
and Tablet Computing devices. It contains the following components:

- Regulators
- White LED
- USB battery charger

This patch adds support for tps65217 mfd device. At this time only
the regulator functionality is made available.

Signed-off-by: AnilKumar Ch <anilkumar@ti.com>
Reviwed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>