[llvm-objdump] - Move getRelocationValueString and dependenices out of the llvm-objdump.cpp

getRelocationValueString is a dispatcher function that calls the
corresponding ELF/COFF/Wasm/MachO implementations
that currently live in the llvm-objdump.cpp file.

These implementations better be moved to ELFDump.cpp,
COFFDump.cpp and other corresponding files, to move platform specific
implementation out from the common logic.

The patch does that. Also, I had to move ToolSectionFilter helper
and SectionFilterIterator, SectionFilter to a header to make them
available across the objdump code.

Differential revision: https://reviews.llvm.org/D56842

llvm-svn: 351545