usb: dwc3: Add dwc3_init/remove with DM_USB

The patch is preparing dwc3 core for enabling DM_USB with peripheral
driver with using driver model support.
The driver will be bound by the DWC3 wrapper driver based on the
dr_mode device tree entry.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
(Remove dwc3-omap changes)
Signed-off-by: Michal Simek <michal.simek@xilinx.com>