Merge the following revs from NetBSD (in an attempt to bring new material

Merge the following revs from NetBSD (in an attempt to bring new material
in in a more piecemeal fashion):

1.105   NOT APPLICABLE TO DRAGONFLY.  This rev moved interrupt enablement
	to near the end of the init.  DragonFly already goes even further
	and moves interrupt enablement into the PCI module.

1.104   Constification and variable naming cleanup.

1.103   Make sure all physical addresses are filled in the qTD even when we have
        a page offset.

1.102   Make sure to honor the USBD_FORCE_SHORT_XFER flag and generate an empty
        transfer when necessary.