extcon: int3496: Add support for controlling Vbus through a regulator

On some boards the 5V vboost-regulator for powering devices connected to
the micro USB connector is not controlled through a GPIO. This happens
for example when the 5V vboost-regulator is integrated into the charger IC
and controlled over I2C.

Add support for controlling the 5V vboost-regulator through the regulator
framework for such boards.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>