Handle prefixes before fwait

0x9b (fwait) is both an instruction and an opcode prefix.  When 0x9b is
treated as an instruction, we need to handle any prefixes before it.
This patch handles it properly.

gas/testsuite/

	PR binutils/16891
	* gas/i386/opcode.s: Add test for fwait with prefix.
	* gas/i386/opcode-intel.d: Updated.
	* gas/i386/opcode-suffix.d: Likewise.
	* gas/i386/opcode.d: Likewise.

opcodes/

	PR binutils/16891
	* i386-dis.c (print_insn): Handle prefixes before fwait.