[X86] Ignore bits 2:0 of the modrm byte when disassembling lfence, mfence, and sfence.

These are documented as using modrm byte of 0xe8, 0xf0, and 0xf8
respectively. But hardware ignore bits 2:0. So 0xe9-0xef is treated
the same as 0xe8. Similar for the other two.

Fixing this required adding 8 new formats to the X86 instructions
to convey this information. Could have gotten away with 3, but
adding all 8 made for a more logical conversion from format to
modrm encoding.

I renumbered the format encodings to keep the register modrm
formats grouped together.