x86_64 should just work as it is in the same group as x86

x86_64 seems to work on my system (basic blocks/graph layout). That's consistent with the fact that the "x86-specific" code for Capstone has both x86 and x86_64 in the same group. If the only thing we need for static support for other architectures is modifications to the disasm.py, I'd be happy to go ahead and implement them.