[PATCH] USB: Add dummy_hcd to the main kernel

[PATCH] USB: Add dummy_hcd to the main kernel

This is a resubmission of as225, together with appropriate changes for the
g_serial driver.  David Brownell's latest g_ether update makes it
unnecessary to change that file or gadget_chips.h.

dummy_hcd is simultaneously a host controller driver and a device
controller driver.  It creates a simulated HC together with a simulated
UDC plugged into it.  Gadget drivers can run under the simulated UDC and
will appear as regular USB devices on the simulated HC.  The simulation is
reasonably (although not totally) realistic.

It's a wonderful tool for testing and developing gadget drivers without
the need for lots of additional hardware: Both the host driver and the
gadget driver can run on the same computer.  It's been available for quite
some time in David's gadget-2.6 tree and it works well.  I couldn't have
gotten the file-storage gadget running in any reasonable length of time
without it.