READ/WRITE_DEVICE*_HANDLERs are now passed an
address_space &, and the 8-bit variants get a mem_mask
as well. This means they are now directly compatible
with the member function delegates. Added a generic
address space to the driver_device that can be used
when no specific address space is available. Also
added DECLARE_READ/WRITE_DEVICE*_HANDLER macros to
declare device callbacks with default mem_mask
parameters. [Aaron Giles]
