staging: comedi: addi_apci_1500: tidy up PCI Bar 1 register map

For aesthetics, convert the enum for the PCI Bar 1 register map to
defines and move them to the main driver source file. Rename the
registers.

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>