menuconfig: Show all symbols at each menu location for multi.def. choices
menuconfig: Show all symbols at each menu location for multi.def. choices

For named choices defined in multiple locations, show the symbols from
all locations, regardless of via which menu node the choice is entered.

Named choices with symbols in more than one location are broken in the C
tools, so there's no reference for the behavior here. This behavior
probably makes more sense than just showing the choice symbols at the
current location at least, which was the old behavior in Kconfiglib's
menuconfig.

Suggested by Mitja Horvat (pinkfluid).

ulfalizer/Kconfiglib,ulfalizer/Kconfiglib