USB: ohci: da8xx: Allow a regulator to handle VBUS

Using a regulator to handle VBUS will eliminate the need for
platform data and callbacks, and make the driver more generic
allowing different types of regulators to handle VBUS.

The regulator equivalents to the platform callbacks are:
    set_power   ->  regulator_enable/regulator_disable
    get_power   ->  regulator_is_enabled
    get_oci     ->  regulator_get_error_flags
    ocic_notify ->  regulator event notification

Signed-off-by: Axel Haslam <ahaslam@baylibre.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>