examples/multi_process: add SPDX license tag to makefiles

examples/multi_process: add SPDX license tag to makefiles

The makefiles for some of the multi_process example files were missing
SPDX license headers, so add them. These Makefiles completely replaced
the older makefiles and were written from scratch, not based on previous
versions, so add a new copyright year on them.

Fixes: 13abe17c3cd4 ("examples/multi_process: convert to pkg-config-based build")

Suggested-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>