regulator: tps6507x: add device tree support.

Add device tree based initialization support for
TI's tps6507x regulators.
Add device tree binding document for TI's tps6507x
using datasheet:
http://www.ti.com/lit/ds/symlink/tps65070.pdf



Signed-off-by: Vishwanathrao Badarkhe, Manish <manishv.b@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>