staging: comedi: ni_tio: tidy up Gxx_Interrupt_Acknowledge_Bits

Convert this enum and the others related to it into defines and
rename the CamelCase symbols.

For aesthetics, move the new defines so they are associated with
the register define.

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>