Change tblgen to emit FOOISD opcode names as two

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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@99494 91177308-0d34-0410-b5e6-96231b3b80d8