staging: comedi: addi_tcw.h: provide generic defines for the ADDI-DATA TCW

The TCW (timer/counter/watchdog) devices in the various ADDI-DATA drivers
use a common register map definition. Provide a common generic define for
these registers so they don't have to be replicated in each driver.

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>