usb: gadget: udc-core: remove manual dma configuration

Since commit 7ace8fc8 ("usb: gadget: udc: core: Fix argument of
dma_map_single for IOMMU") it is not necessary to configure DMA for
usb_gadget device manually, because all DMA operation are performed
using parent/controller device.

Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>