[dev][usb-bus] Refactor usb-bus driver

Previously the usb-bus driver not only managed all USB devices for a USB controller
but also managed creating devmgr devices for each interface on each device.
Now the usb-bus driver only creates devmgr devices for each USB device.
The functionality of creating devmgr devices for USB interfaces is handled by
a new driver called usb-composite, which binds to the devices created by the
usb-bus driver.

We add a new protocol ZX_PROTOCOL_USB_DEVICE to represent a USB device
(the existing ZX_PROTOCOL_USB protocol is used to represent a USB interface).
For now ZX_PROTOCOL_USB_DEVICE and ZX_PROTOCOL_USB both share the same protocol
interface (defined in ddk/protocol/usb.h), but this protocol will be refactored
in an upcoming CL.

The combination of the new usb-bus and usb-composite drivers implement
the same functionality as the old usb-bus driver, so no changes are needed
for existing USB drivers. However drivers have the option of binding directly
to the ZX_PROTOCOL_USB_DEVICE protocol in cases where the driver needs full control
of the USB device. For example, a USB device might have several interfaces that
all need to be accessed by the same driver. In this case, we do not want the
usb-composite driver to create devices for each interface.
To avoid this, the driver can bind to the ZX_PROTOCOL_USB_DEVICE device provided
by the usb-bus driver instead of the usb-composite driver.
The usb-composite driver is marked as a fallback driver to allow that to happen.

Drivers that bind directly to usb-bus with the ZX_PROTOCOL_USB_DEVICE protocol
must do some additional work that is usually handled by usb-composite.
In particular, they must call usb_enable_endpoint() to enable the endpoints
they are using.

In addition to the above, there are some changes to the ioctl interface for USB.
/dev/class/usb-device now contains files for all the USB devices created by the
usb-bus driver. Tools like lsusb should now use this directory instead of
/dev/class/usb.

The devices representing USB interfaces no longer support ioctl. To support that change,
some calls to device_ioctl() have been replaced with protocol calls.
IOCTL_USB_GET_CURRENT_FRAME is replaced by a new usb_get_current_frame() function in the USB protocol.

To help test this new functionality, the usb-hub driver now binds to ZX_PROTOCOL_USB_DEVICE
rather than ZX_PROTOCOL_USB. This means the usb-hub driver binds directly to usb-bus,
with no usb-composite support in between.

TEST: USB on NUC and VIM2 is working as expected. Tested keyboards, USB 2.0 and 3.0 hubs,
mass storage and USB audio.

Change-Id: Ib9f5aa09f8c0ae7ae2e7378f6996181fce5afb11

[uapp][usb-test-fwloader] Print updated version.

TEST= fx shell usb-test-fwloader firmware.img

Change-Id: Ia4846086987a8f99c0a7f5d8dd8f6c42a15b24d9

[uapp][usb-test-fwloader] Add updating usb-tester.

If there is no FX3 device connected, we try to look for a usb-tester
device, and set it to fwloader mode. This will cause it to re-enumerate
as a FX3 device and we can then load the new firmware.

TEST= plug in FX3 device
fx shell usb-test-fwloader firmware.img
fx shell usb-test-fwloader updated-firmware.img
runtests -t usb-test

Change-Id: If5ebc75461b14bd07ab911ea59fbc7155b3de336

[dev][fx3] Loads firmware onto FX3 for usb testing.

The usb-test-fwloader app reads the firmware image into a vmo,
and passes the vmo to fx3 to load and run.

TEST= plug in FX3 board, copy firmware image to zircon and run
fx shell usb-test-fwloader firmware.img

Change-Id: I472121179c92686574e888c85be026bc5eae081c