mk: do post processing on objects that register a driver

Modify the compilation makefile to identify C files that export PMD
information, and use that to trigger execution of the pmdinfo binary.  If
the execution of pmdinfo is successful, compile the output C file to an
object, and use the linker to do relocatable linking on the resultant
object file into the parent object that it came from.  This effectively
just adds the json string into the string table of the object that defines
the PMD to the outside world.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Panu Matilainen <pmatilai@redhat.com>
Acked-by: Remy Horton <remy.horton@intel.com>