staging: comedi: ni_660x: cleanup the NI660X_IO_CFG register helpers

Convert the inline functions used to set the bits in the NI600X_IO_CFG
registers into macros. Also convert the enum ni_660x_pfi_output_select
into defines. This clarifies the association with the register.

This also fixes a number of checkpatch.pl issues about:

WARNING: Prefer 'unsigned int' to bare use of 'unsigned'

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>