usb: gadget: Add UDC driver for tegra XUSB device mode controller

This patch adds UDC driver for tegra XUSB 3.0 device mode controller.
XUSB device mode controller supports SS, HS and FS modes

Based on work by:
  Mark Kuo <mkuo@nvidia.com>
  Hui Fu <hfu@nvidia.com>
  Andrew Bresticker <abrestic@chromium.org>

Signed-off-by: Nagarjuna Kristam <nkristam@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>