Isolate Target-specific functionality of DataExtractor.

In an effort to move the various DataBuffer / DataExtractor
classes from Core -> Utility, we have to separate the low-level
functionality from the higher level functionality.  Only a
few functions required anything other than reading/writing
raw bytes, so those functions are separated out into a
more appropriate area.  Specifically, Dump() and DumpHexBytes()
are moved into free functions in Core/DumpDataExtractor.cpp,
and GetGNUEHPointer is moved into a static function in the
only file that it's referenced from.

Differential Revision: https://reviews.llvm.org/D30560

llvm-svn: 296910