[dev][usb] Add usb_reset_device and XHCI changes.

After usb-hub does the port reset, XHCI sends TRB_CMD_RESET_DEVICE.
We also need to address the device again.

I extracted part of xhci_handle_enumerate_device into a new
function xhci_setup_slot, as it is the same thing as xhci_reset_device
has to do after the reset.

This is so we can load new firmware on the USB ML device.

ZX-3155 #comment

TEST= plugged in USB ML device, ran usb-fwloader -d -f firmware and
verified the device descriptor changed.

Also tried resetting in the usb audio driver and running audio -d 1 tone

Change-Id: Id3bd748c0d40838d98e233ad1f01589cb1042021