extcon: mrfld: Introduce extcon driver for Basin Cove PMIC

On Intel Merrifield the Basin Cove PMIC provides a feature to detect
the USB connection type. This driver utilizes the feature in order
to support the USB dual role detection.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>