[AArch64] Print instruction before atomic semantic annotations

Commit r353303 added annotations when acquire semantics
were dropped from an instruction.

printAnnotation was called before printInstruction.
So if you didn't set a separate comment output stream
you got <comment><instr> instead of <instr><comment>
as expected.

To fix this move the new printAnnotation to after
the instruction is printed.

Differential Revision: https://reviews.llvm.org/D58059

llvm-svn: 354565