[PATCH] D13360: [llvm-objdump] Teach -d about AArch64 mapping symbols

AArch64 uses $d* and $x* to interleave between text and data.
llvm-objdump didn't know about this so it ended up printing garbage.
This patch is a first step towards a solution of the problem.

Differential Revision:	 http://reviews.llvm.org/D13360

llvm-svn: 249083