Fix x86_64 instruction formatting for >2 operands

[kupsch]

Formatting an x86_64 instruction with three or more operands has the operands in the wrong order. Dyninst stores the operands in intel syntax order, but wants to formats them in AT&T syntax order. Essentially the formatter rotates the operands right one instead of reversing the list. If the intel order was A, B, C, the AT&T syntax should be C, B, A, but it currently outputs as C, A, B. One and two operand instructions format correctly as rotating and reversing produce the same result.