device_memory_interface::space() assert against NULL and
return a reference, and pushed references throughout all
address space usage in the system. Added a has_space()
method to check for those rare case when it is ambiguous.
[Aaron Giles]
Also reinstated the generic space and added fatal error
handlers if anyone tries to actually read/write from it.
and set_state() to set_state_int() for consistency.
Update all callers. Also add set_pc() helper and updated
all callers to use that instead of set_state_int(STATE_GENPC)
[Aaron Giles]
Added device_t::state() method to get the state interface.
Added redundant device_state_interface::state() method to
catch redundant use of it. [Aaron Giles]
Removed cpu_get_reg() and cpu_set_reg() macros in favor of
using the above methods. [Aaron Giles]
