menuconfig/genrest: Exclude implicit submenus from menu paths

Make all menu paths ("(top menu) -> menu -> submenu -> ...") exclude
implicit submenus, which are shown indented in the menuconfig interface
and are created when items depend on the symbol before them.

Previously, implicit submenus were excluded in the menu path at the top
of the menuconfig interface, but were included in the menuconfig symbol
information dialog and in the docs generated by genrest.py.

This makes it consistent, and un-spams the documentation for some
symbols a bit.

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