usb: gadget Kconfig cleanup

This reorders the list of USB peripheral controller drivers so it's
more common for the initial (default) value to be relevant:  put the
SOC integrated silicon up front, discrete stuff last.  Alphabetize.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>