usb: gadget: hsotg: pullup method implementation for s3c-hsotg UDC driver

This commit adds pullup method implementation for UDC s3c-hsotg driver.
It is needed for e.g. CCG - Configurable Composite Gadget, when user space
configuration change request device disconnection from USB bus (done via
calling usb_gadget_connect/disconnect, which calls UDC's pullup method).

Implementation of pullup method has caused removal of phy_enable and
core_init methods from udc_start to pullup.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>