staging: comedi: ni_660x: cleanup the NI660X_GLOBAL_INT_{STATUS, CFG}

Remove the enums global_interrupt_{status,config}_register_bits and
add defines for the CamelCase values.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>