AArch64: Add basic relocation processing for llvm-dwarfdump.

This allows llvm-dwarfdump to handle the relocations needed, at least
for LLVM-produced code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174874 91177308-0d34-0410-b5e6-96231b3b80d8