staging: comedi: comedi_8254: introduce module for 8254 timer support

staging: comedi: comedi_8254: introduce module for 8254 timer support

A 8254 timer/counter is commonly used on data acquisition boards to provide
the internal pacer clock used to acquire analog input samples. Some boards
also to allow the timers to be used externally.

Currently the 8254 timers are supported by comedi using the 8253.h header
and a number of inline functions. This works for the internal pacer clock
but requires the drivers to implement subdevice code necessary to use the
timers externally.

Introduce a new module to support both the internal pacer clock and the
external counter subdevice. This will allow removing a bunch of duplicated
code in the drivers and standardizes the comedi 8254 timer support.

This implementation is based on the 8253.h inline functions and the various
subdevice functionality in the comedi drivers.

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>