usb: gadget: s3c-hsotg: get phy bus width from phy subsystem

Adds support for querying the phy bus width from the generic phy
subsystem. Configure UTMI bus width in GUSBCFG based on this value.

Signed-off-by: Matt Porter <mporter@linaro.org>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>