regulator: lp8755: new driver for LP8755

This patch is for new lp8755 regulator dirver and
several unsed variables were deleted and then test was done.

LP8755 :
The LP8755 is a high performance power management unit.It contains
six step-down DC-DC converters which can can be filexibly bundled
together in multiphase converters as required by application.
www.ti.com

Signed-off-by: Daniel Jeong <gshark.jeong@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>