usbcore: move code among source files

This revised patch (as713b) moves a few routines among source files in
usbcore.  Some driver-related code in usb.c (claiming interfaces and
matching IDs) is moved to driver.c, where it belongs.  Also the
usb_generic stuff in driver.c is moved to a new source file: generic.c.
(That's the reason for revising the patch.)  Although not very big now,
it will get bigger in a later patch.

None of the code has been changed; it has only been re-arranged.


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