regulator: add voltage selection capability to mc13783 regulators v2 .

This patch, complete the mc13783 regulator subsystem driver with
voltage selecting capability.
Main Switches (SW1AB, SW2AB) are not supported yet.

version 2 diffs:
- delete the "Switchers PLL" enable and multiplication factor value
  selecting capability because it is not a voltage or current regulator.
  This will be a part of Main switcher supporting task.
- Correct many coding style problems pointed me out.

Signed-off-by: Alberto Panizzo <maramaopercheseimorto@gmail.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>