usb: gadget: s3c-hsotg: enable generic phy support

Adds support for the generic PHY subsystem. Generic PHY
support is probed and then the driver falls back to checking
for an old style USB PHY and pdata if not found.

Signed-off-by: Matt Porter <mporter@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>