Reorganize Makefile with sections and guide

Over several years the podman Makefile has become a
bloated complex mess.  This impedes both debugging
and maintenance, besides causing general eye-strain.

Fix this by adding a simple navigation/layout guide, to help
developers quickly find what's needed. Re-organize the entire
file according to the new layout guide.  Add section headers
that call out the purpose of the encompassed content, and
are easy to locate with search-tools.

Note: No recipes or definitions have been altered by this
commit, only re-arranged.

Signed-off-by: Chris Evich <[email protected]>