[dev][usb][dwc3] First cut at DWC3 USB controller driver

Implements basic peripheral mode support for DWC3

Still to do for peripheral mode:
- USB 3 support
- Isochronous endpoint support
- Scatter/gather support
- OTG support for better connect/disconnect detection

and beyond peripheral mode:
- USB host support (we will layer the XHCI driver on top of this driver for host support)
- role switching between host and peripheral mode
- power management

Change-Id: I028f7af18f4434e17e1fe5fe36f0d1a83a409e55