Change tblgen to emit FOOISD opcode names as two

bytes instead of one byte.  This is important because
we're running up to too many opcodes to fit in a byte
and it is aggrevated by FIRST_TARGET_MEMORY_OPCODE
making the numbering sparse.  This just bites the
bullet and bloats out the table.  In practice, this
increases the size of the x86 isel table from 74.5K
to 76K.  I think we'll cope :)

This fixes rdar://7791648

llvm-svn: 99494