Create hierarchical demo Makefile.

Create hierarchical demo Makefile.

Adds a Makefile with all, clean, and test targets.
This has only been added for demos that already contain Makefiles.
For problematic tests that require inputs, the test target does nothing.

(Note: Demos should be self contained and not require unknown external
inputs. This PR does not attempt to fix this.)

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20546)