This patch support the extcon property for the external connector
because each external connector might have the property according to
the H/W design and the specific characteristics.

- EXTCON_PROP_USB_[property name]
- EXTCON_PROP_CHG_[property name]
- EXTCON_PROP_JACK_[property name]
- EXTCON_PROP_DISP_[property name]

Add the new extcon APIs to get/set the property value as following:
- int extcon_get_property(struct extcon_dev *edev, unsigned int id,
			unsigned int prop,
			union extcon_property_value *prop_val)
- int extcon_set_property(struct extcon_dev *edev, unsigned int id,
			unsigned int prop,
			union extcon_property_value prop_val)
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Tested-by: Chris Zhong <zyw@rock-chips.com>
Tested-by: Guenter Roeck <groeck@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>