Move `labpc_drain_dma()` into the "ni_labpc_isadma" module. Provide a
dummy inline function in "ni_labpc_isadma.h" if the module is not being
built.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>