staging: comedi: ni_stc.h: final cleanup

1) Move the enum's to a better location and tidy up the whitespace.
2) Tidy up the defines used for some array sizes in the private data.
3) Add comments for the spinlock_t variables in the private data.
4) Move the forward declaration to the end of the file.

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>