extcon: add extcon-odroid-usbotg driver

extcon: add extcon-odroid-usbotg driver

This patch adds extcon driver for Odroid U3, U3+ and X boards.
It recognizes type of USB cable connected to Odroid board basing on
two signal lines VBUS_DET and OTG_ID (the second one is present only
on Odroid U3+ board).

Following table of states presents relationship between this signals
and detected cable type:

state    | VBUS_DET |  OTG_ID
-------------------------------
USB      |    H     |    H
invalid  |    H     |    L
disconn. |    L     |    H
USB-Host |    L     |    L

This driver is based on extcon-gpio driver.

Signed-off-by: Łukasz Stelmach <l.stelmach@samsung.com>
Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>