[llvm-readobj] - Simplify conditions used for printing segment mappings. NFCI.

This patch is a NFC refactoring.

Currently the logic is overcomplicated, contains dead conditions and is very hard to read.
This patch performs a very straightforward simplification. Probably it can be
simplified and improved more, but we need to land test cases documenting/testing
all the current functionality first.

Differential revision: https://reviews.llvm.org/D78709