[obj2yaml] - Dump the sh_entsize section field.

I faced with the fact that obj2yaml does not dump the sh_entsize field.
A problem arose when I tried to dump ELF versioning sections.

This is close to what D50235 did, but D50235 did the change for yaml2obj, and now
I had to do the same for obj2yaml.

Differential revision: https://reviews.llvm.org/D57229

llvm-svn: 352373