staging: comedi: comedidev.h: don't expose COMEDI_CB_* defines to userspace

The COMEDI_CB_* defines are the comedi_async "events" that the drivers set
to let the core detect the state of running async commands. These "events"
are only relevant to the kernel modules and should not be exposed to
userspace in the comedi.h user API header.

Move the defines to comedidev.h to avoid exposing them. For aesthetics,
convert the defines to bit shifts to better indicate that they are bitmask
values. Cleanup the documentation.

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>