USB: remove struct usb_operations

All of the currently-supported USB host controller drivers use the HCD
bus-glue framework.  As part of the program for flattening out the glue
layer, this patch (as769) removes the usb_operations structure.  All
function calls now go directly to the HCD routines (slightly renamed
to remain within the "usb_" namespace).

The patch also removes usb_alloc_bus(), because it's not useful in the
HCD framework and it wasn't referenced anywhere.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>