GPU implementation of HexahedronFEMForceField compatible with async solvers

git-svn-id: svn://scm.gforge.inria.fr/svnroot/sofa/trunk@10790 b7f1a160-662a-0410-a6d8-bea165342f16
Optization for CudaHexahedronFEMForceField

git-svn-id: svn://scm.gforge.inria.fr/svnroot/sofa/trunk@10791 b7f1a160-662a-0410-a6d8-bea165342f16