Missing x86 mnemonics and registers (self-hosted backend encoder)

[Arnau478]

There are some assembly instruction mnemonics missing on the x86 backend, specially some CPL0 instructions like cli, sti, wrmsr, rdmsr, hlt, ltr, lidt, iretq, hlt... There are some registers missing too, namely the control registers (cr0, cr2, and so on).