[zircon][usb-request]Move usb-request.c out of ulib/ddk

The motivation behind this changes is that eventually system/ulib/ddk
should go away and parts of it should move to where they belong.
This changeset moves usb-request.c, usb-request-test.c out of the ulib/ddk
to system/dev/lib/usb-request. This library is internal for system/dev/usb
and all its fucntionality will be exposed via the usb protocol and the
usb-function protocol to the client drivers.

Test: Build. Basic Sanity test on vim2. Ran usb-request-tests using
runtests /boot/test/ddk/driver-tests

Change-Id: Ia62693f51046b9c93e4a4b9abfd25286b0d9b972

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[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