We have proper encoding facilities to encode operands and instructions;
there's no need to pollute the MC representation with encoding details.
Supposed to be an NFCI, but happens to fix some re-encoded instruction
codes in disassembler tests.
The 64-bit operands are to be addressed in following patches introducing
MC-level representation for lit() and lit64() modifiers, to then be
respected by both the assembler and disassembler.
7ba7021951