genrest: Include all parents in menu paths

Previously, symbols not defined with 'menuconfig' with children weren't
listed in the children's menu paths. It was deliberate, but it's
probably an anti-feature in retrospect, because it can make it harder to
find stuff by following the menu path.

Don't try to be clever and just list all the parent nodes in the menu
path.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>