For config-only components, component.mk should now contain "COMPONENT_CONFIG_ONLY := 1"
Also refactored some of the generation of linker paths, library list. This required cleaning up the way the bootloader
project works, it's now mostly independent from the parent.
Each COMPONENT_DIRS directory can now either be a component directory, or a parent directory containing component
subdirectories.
When searching for components, skip any directory which doesn't have component.mk, Kconfig.projbuild, or
Makefile.projbuild in it. This helps with debugging, list-components output, etc.
