FreeBSD seems to be hanging when it tries to load the ehci driver. The ehci driver is what controls the USB 2.0 bus. It is enabled in the GENERIC kernel. If you disable USB 2.0, things like your USB harddrive probably won't work because they require the USB 2.0 bus.
I'd suggest asking on the
FreeBSD USB Mailing List. Be sure to include a full dmesg and as much detail as possible.