[llvm-readobj] Separate `Symbol Version` dumpers into `LLVM style` and `GNU style`

Summary:
Currently, llvm-readobj can dump symbol version sections only in LLVM style. In this patch, I would like to separate these dumpers into GNU style and 
LLVM style for future implementation.

Reviewers: grimar, jhenderson, mattd, rupprecht

Reviewed By: jhenderson, rupprecht

Subscribers: ormris, dyung, RKSimon, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59186

llvm-svn: 356881