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This adds support to stm32's mboot for the Microsoft WCID USB 0xee string
and Compatible ID Feature Descriptor.  This allows the USB device to
automatically set the default USB driver, so that when the device is
plugged in Windows will assign the winusb driver to it.  This means that
USB DFU mode can be used without installing any drivers.

For example this page will work (allow the board to be updated over DFU)
with zero install: https://devanlai.github.io/webdfu/dfu-util/

Tested on Windows 10, Windows can read the 0xee string correctly, and
requests the second special descriptor, which then configures the USB
device to use the winusb driver.
Signed-off-by: Damien George <damien@micropython.org>