usb: gadget: udc: core: add usb_gadget_{un}map_request_by_dev()

If the following environment, the first argument of DMA API should
be set to a DMAC's device structure, not a udc controller's one.
 - A udc controller needs an external DMAC device (like a DMA Engine).
 - The external DMAC enables IOMMU.

So, this patch add usb_gadget_{un}map_request_by_dev() API to set
a DMAC's device structure by a udc controller driver.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>