nm: also retrieve size for COFF function symbols

Like ELF for all symbols, COFF can record size for at least function
ones. Use that - if available - in preference to the distance-to-next-
symbol heuristic.

To be able to use the new test there, make TI C54x follow TI C4x in
providing .sdef to cover for .def already having different meaning.
5 files changed