USB: at91_udc, shrink runtime footprint

This is a runtime codespace shrink:  in most cases, platform devices should
put probe() should in the init section, and remove() in the exit section.
And I have no idea why the module init/exit routines were mismarked.
It also moves one function table into read-only data.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>