Fix armthumb disasm, 64bit inc/dec on x86, syscall in r_asm

- rasm2 -k to select kernel like ragg2 does
- rasm2 -k linux -b32 'mov eax, $sys.write'
- Implement x86-64bit INC and DEC
- Add x86-8 and x86-64 bit calling conventions in r_syscall