Added doxygen comments to geopm_message.h
Added doxygen comments to geopm_message.h

Signed-off-by: Steve S. Sylvester <b0839a0405c3f908ea9b10b668e5564aefda5af5@intel.com>

geopm/geopm,cmcantalupo/geopm,geopm/geopm,geopm/geopm,sssylvester/geopm,geopm/geopm,sssylvester/geopm,geopm/geopm,cmcantalupo/geopm,cmcantalupo/geopm,sssylvester/geopm,cmcantalupo/geopm,cmcantalupo/geopm,sssylvester/geopm