[MachineFunction] Base support for call site info tracking

Add an attribute into the MachineFunction that tracks call site info.

([8/13] Introduce the debug entry values.)

Co-authored-by: Ananth Sowda <asowda@cisco.com>
Co-authored-by: Nikola Prica <nikola.prica@rt-rk.com>
Co-authored-by: Ivan Baev <ibaev@cisco.com>

Differential Revision: https://reviews.llvm.org/D61061

llvm-svn: 364506