Make entire submenus selectable

From Crashcourse Wiki

If an entire submenu of the kernel Kbuild hierarchy can be selected or deselected in its entirety, you should be able to do that without having to enter that subdirectory during configuration.

As an example, consider the bottom of the MTD configuration menu -- you can configure OneNAND support at the MTD menu level, but to configure LPDDR or UBI, you need to enter those submenus to turn them on or off, which is kind of a waste of time.

Compare the Kconfig file for OneNAND with those of LPDDR and UBI to see the difference but make sure that the restructured menu entry is exactly equivalent.