regulator: oledb-regulator: Add OLEDB regulator device driver

The OLEDB module provides the AVDD bias supply for the AMOLED display.
The supported voltage range of the bias is 5 to 8.1V. This driver provides
the regulator interface to control the bias voltage.

Change-Id: Ide4af995ca9fd12b3467de42e5d08eddc3981344
Signed-off-by: ansharma <ansharma@codeaurora.org>
Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>