Improve DWARFDebugFrame::parse to also handle __eh_frame.

Improve DWARFDebugFrame::parse to also handle __eh_frame.

LLVM MC has single methods which can handle the output of EH frame and DWARF CIE's and FDE's.

This code improves DWARFDebugFrame::parse to do the same for parsing.

This also allows llvm-objdump to support the --dwarf=frames option which objdump supports.  This
option dumps the .eh_frame section using the new code in DWARFDebugFrame::parse.

http://reviews.llvm.org/D15535

Reviewed by Rafael Espindola.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256008 91177308-0d34-0410-b5e6-96231b3b80d8