comedi: ni_routing: tools: Update due to moved COMEDI headers

comedi: ni_routing: tools: Update due to moved COMEDI headers

Building of the tools for converting the NI routing information between
CSV files (for maintenance) and C files (for building) was broken by the
move of the main COMEDI header files to "include/uapi/linux/" and
"include/linux/".  (These tools are not built as part of the normal
kernel build process.)  Fix it in the Makefile.

A slight niggle is that `#include <linux/comedi.h>` needs to work when
compiling the `convert_c_to_py` program, but it cannot use a `-I` option
referring to the "uapi" include directory because that interferes with
inclusion of other system headers.  So it uses `-I.` and makes a local
copy (actually a symbolic link) as "./linux/comedi.h".

Also remove some unneeded cruft such as the `-D"BIT(x)=(1<<(x))"`
preprocessor flag.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20211117120604.117740-3-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>