usb: gadget: s3c-hsudc: Add regulator handling

The udc has three supplies: vdda (3.3V), vddi (1.2V) and vddosc (1.8-3.3V).
Turn these on and off on start and stop calls.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>