[X86][Disassembler] Shrink X86GenDisassemblerTables.inc from 36M to 6.1M

In x86Disassembler{OneByte,TwoByte,...}Codes,
"/* EmptyTable */" is very common. Omitting it saves lots of space.
Also, there is no need to display a table entry in multiple lines.

It is also common that the whole OpcodeDecision is { MODRM_ONEENTRY, 0}.
Make use of zero-initialization.