uhci intr setup

[Sepherosa Ziehau]

Hi all,

Setup intr in the last step of uhci_pci_attach():
http://leaf.dragonflybsd.org/~sephe/uhci_pci.c.diff

This can shut up the "livelock!" complaining (only during system
starting up) on my test box while a USB ethernet card is attached.

I think it also can (reliably) prevent uhci_intr() from being called
before uhci_init() and children's attachment

Hope I didn't walk on other folk(asmodai)'s toe.
Please review it.

Best Regards,
sephe

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