power: supply: bq25890: Add support for registering the Vbus boost converter as a regulator

The bq25890_charger code supports enabling/disabling the boost converter
based on usb-phy notifications. But the usb-phy framework is not used on
all boards/platforms. At support for registering the Vbus boost converter
as a standard regulator when there is no usb-phy on the board.

Also add support for providing regulator_init_data through platform_data
for use on boards where device-tree is not used and the platform code must
thus provide the regulator_init_data.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>