[x86] Remove unused classes from tablegen instruction info.
[x86] Refactor some tablegen instruction info classes slightly to prepare for another change. NFC.
[X86] Add the 0x82 instructions to the disassebmler. They are identical in functionality to the 0x80 opcode instructions, but are not valid in 64-bit mode.
[X86] Fix some cases where some 8-bit instructions were marked as being convertible to three address instructions, but aren't really.