x86: CPU-qualify {disp16} / {disp32}

x86: CPU-qualify {disp16} / {disp32}

{disp16} is invalid to use in 64-bit mode, while {disp32} is invalid to
use on pre-386 CPUs. The latter, also affecting other (real) prefixes,
further requires that like for insns we fully check the CPU flags; till
now only Cpu64/CpuNo64 were taken into consideration.