macOS Guest Reading USB 3.0 Bus as USB 2.0

This bug has been copied automatically from: https://bugs.launchpad.net/qemu/+bug/1708551
Reported by 'Divine E' on 2017-08-03 :

Description:
I'm having trouble with USB Passthrough. Running `system_profiler
SPUSBDataType` on macOS guest confirms that the system "sees" my device,
and that qemu is passing *something* through. However, the system sees my
connection as USB 2.0, even though i'm passing through XHCI controllers
(nec-usb-xhci/qemu-xhci). I suspect this is the reason why my guest is
unable to recognize my iPhone in XCode & iTunes.

Parameters:
QEMU release version: 2.10.0-rc0
Bios: [patched version of
OVMF](https://github.com/gsomlo/edk2/tree/macboot)]
Command Line: https://pastebin.com/pBSYbrW1
Host: Arch Linux
Guest: macOS v10.12.6
Guest System Info: https://pastebin.com/U1Tihxei

Notes:
1. Observed sometime after late-May-early-June of this year.

2. Due to [a defect in qemu v2.8 which affected GTK
users](https://bugs.launchpad.net/qemu/+bug/1578192), and [a recent change
to macOS' booting process conflicting with qemu
v2.9](https://lists.nongnu.org/archive/html/qemu-
devel/2017-03/msg06366.html), i'm forced to use qemu v2.10.0-rc0 (as -rc1
fails to load OVMF right now).