treewide: rearrange source directories

treewide: rearrange source directories

The src directory containing lib and tools is not necessary and will
actually cause problems if we tried to add a new component to src/
which would depend on libraries from the bindings directory because it
(bindings) already depends on src/lib.

Simplify the directory structure. Move lib and tools to the root source
directory and update all relevant files. That way we can specify the
exact build order of components from the top source Makefile.am.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>