[X86] Increase X86_MAX_OPERANDS from 5 to 6

This controls the number of operands in the disassembler's x86OperandSets
table.  The entries describe how the operand is encoded and its type.

Not to surprisingly 5 operands is insufficient for AVX512.  Consider
VALIGNDrrik in the next patch.  These are its operand specifiers:

  { /* 328 */
    { ENCODING_DUP, TYPE_DUP1 },
    { ENCODING_REG, TYPE_XMM512 },
    { ENCODING_WRITEMASK, TYPE_VK8 },
    { ENCODING_VVVV, TYPE_XMM512 },
    { ENCODING_RM_CD64, TYPE_XMM512 },
    { ENCODING_IB, TYPE_IMM8 },
  },

llvm-svn: 214889