ART: PassMEDataHolder should have a data field

For passes that would like to pass data around while working, let them actually
  allocate it if need be in the Start, use it during the Worker, and
  potentially free it during the End.

Change-Id: I03238ef17158f7e2615d6defe5d7f15432c8a511
Signed-off-by: Jean Christophe Beyler <jean.christophe.beyler@intel.com>