[llvm-readobj] Generic hex-dump option

[llvm-readobj] Generic hex-dump option

Helpers are available to make this option file format independant. This
patch adds the feature for Wasm file format. It doesn't change the
behavior of the other file format handling.

Differential Revision: https://reviews.llvm.org/D49545

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337896 91177308-0d34-0410-b5e6-96231b3b80d8