staging: comedi: drivers: re-do PLX PCI 9080 DMACSRx register values

Replace the existing macros in "plx9080.h" that define values for the
DMACSR0 and DMACSR0 registers.  Use the prefix `PLX_DMACSR_` for the
macros.  Make use of the `BIT(x)` macro to define the values.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>