llvm-dwarfdump: Do not include address offsets for attributes, only for tags

This reduces the noise in diffs making it more likely that, at least for
LLVM revision-over-revision, diffs will actually yield usable results.

This is consistent with objdump's DWARF dumping behavior.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188650 91177308-0d34-0410-b5e6-96231b3b80d8