staging: comedi: addi_apci_3120: move timer helpers to main driver source

Move the timer read/write and set mode helpers from the included source
file into the main driver source 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>